DCCC684/2017

DCCC684/2017

A A B B DCCC 684/2017 C [2020] HKDC 628 C D IN THE DISTRICT COURT OF THE D HONG KONG SPECIAL ADMINISTRATIVE REGION E E CRIMINAL CASE NO 684 OF 2017 F F --------------------------- G G HKSAR H v H CHAN KIT YI (D1) I I LAU SHEUNG MAN (D2) J ---------------------------- J K K Before: HH Judge K Lo L Date: 29 November 2019 L Present: Mr Kuan Bak On Franco, Senior Public Prosecutor and M M Mr Chan Hing-man Raymond, Public Prosecutor of N the Department of Justice, for HKSAR N Ms Lui Wing Chun Petra, instructed by Francis Kong & Co, O O for the defendants P Offence: [1] & [2] Dealing in arms without a licence (無牌經槍械) P Q Q ----------------------------------------- R REASONS FOR VERDICT R ----------------------------------------- S S T 1. D1 and D2 are jointly charged with two counts of dealing in T arms without a licence contrary to section 14 of the Firearms and U U V V  -2- A A B B Ammunition Ordinance, Cap 238. It is alleged that they, on or about 5 C June 2015 (1st charge) and 3 August 2015 (2nd charge), respectively, at C MH (Trading) Company in Hong Kong, by way of trade or business, dealt D D in arms without a licence, namely selling a stunning device. Both E defendants pleaded not guilty. E F F Prosecution case G G 2. Prosecution has called seven witnesses, the first two being H H DPC48019 (“PW1”) and DPC8607 (“PW2”). Their evidence is largely not I in dispute and is embodied also in the Admitted Facts. I J J 3. The prosecution relied on the expert evidence of Professor K Carmen C Y Poon (“PW3”). They also rely on the evidence of Mr Tang K Kwok Ming (“PW6”) and Chan Tak Kwong James(“PW7”). L L 4. As for Dr Ng Chung Ki (“PW4”) and Dr Chiao Wing Fu M M (“PW5”), both senior forensic pathologists and forensic pathologists, the N N prosecution does not rely on their evidence. They were merely tendered O for cross-examination at the request of the defence. O P Admitted Facts P Q Q 5. Under section 65C of the Criminal Procedure Ordinance, R Cap 221, parties admitted, inter alia, that on 5 June 2015, PW1 posed as a R customer, went to MH Trading Company (the shop) and asked to buy a S S lighter device on display. D1, then a salesperson of the shop, took out a T lighter device of the same model. PW1 then bought the same, Exhibit P1, T from D1, and left the shop. U U V V  -3- A A B B C 6. Likewise, on 3 August 2015, PW2 again posed as a customer C again, went to the shop. Again, D1 was the salesperson there. PW2 D D pointed at a lighter device on display in the glass showcase and inquired E D1 of the same. D1 then took out another similar lighter device from the E cashier countertop and explained to him the said device and demonstrated F F to him how to use the same. G G 7. During this time, D1 pressed down the operating switch of the H H device, Exhibit P2. It showed electric current generated between the metal I tips of the device in form of a blue electric arc. Later, PW2 paid D1 $398 I and bought another lighter device of the same model placed in the cabinet J J in the shop, Exhibit P12. K K 8. Then PW2 revealed his identity and the shop was searched. L L Police seized Exhibit P2 and 24 other lighter devices from within the shop. M M 9. D2 was the owner of the shop at the time of the two offences N N and he was also the employer of D1. He was the one responsible for buying O goods for the shop, including Exhibit P1, P2, P12, and the other seized O exhibits. D1 was employed at the shop since year 2014. Apart from the P P lighter devices, the shop also displayed and sold ornaments like necklaces Q and earrings. Q R R 10. After D1 was arrested, under caution she says that she only S worked there. The lighter arc devices were bought by her boss, D2, and S she did not know anything. D1 had later voluntarily taken part in four T T U U V V  -4- A A B B cautioned interviews. Accurate records of such interviews are Exhibits P7 C to P10. C D 11. D2 was arrested on 4 August 2015. He had voluntarily taken D part in a video-recorded interview. The same is accurately recorded in the E E redacted Exhibit P11 and its transcript Exhibit P11A. F F 12. Parties also agree that a PowerPoint headed, “Probe mode G mechanism.” was issued by Medical and Health Department in June 2017, G H (Exhibit D2) and one of the references referred to in the PowerPoint is, H “Conducted Electrical Weapon Drive - Stun Mode, Skin Rub vs Injection,” I I by Mark W Kroll (Exhibit D3). J J 13. D1 has one previous conviction not similar and D2 has a clear K K record. L L Reports of Dr LAM Wai-kwok M M 14. The reports of Dr Lam Wai Kwok in relation to another case N N involving electric arc lighters with probe separation of 5 millimetres were O also produced under section 65B of Criminal Procedure Ordinance O (Exhibit P22 and P23). P P Q 15. Dr Lam was not called during trial. Q R R 16. In his two reports, he said based on the tests performed by the S COMMS, where the peak-to-peak pulsating voltage generated from the S EUT when connected to resistor load of resistance close to human body T T was measured at 46,799 volts, the same was able to generate electric arcs U U V V  -5- A A B B from the electrodes on the head and the same was able to produce 44,643 C high voltage pulses continuously in three seconds duration, based on the C electrical properties and the electrical characteristics of the EUT, the D D devices are similar to stunning devices. E E 17. It was said also that although there was a protective cover on F top of the EUT, when the protective cover was open, the electrodes on the F head of the EUT were exposed and although the space and the current G G between the 5-millimetre distance electrodes was relatively small, the H electrodes were relatively less exposed, it is still possible to apply the H electrodes of EUT on human and cause shock. I I J 18. It was said that the effect of such device when applied on J humans, depend on the number of factors such as the site and duration of K K the application, tolerance to pain and psychological preparedness. It was L said that generally, if applied on an average healthy person on brief L application, subject could be startled and would experience intense local M M pain and muscle spasm. If the application lasts 3 to 5 seconds, the subject N N may fall onto the ground due to muscle paralysis and remain dazed, weak O or even immobilised for a while, possibly up to several minutes. O P P 19. He mentioned that while a Taser will last for 5 seconds, some Q models of stun devices lack features which guarantee a substantive Q discharge and so result in brief electric shock resulting in local pain and R R muscle spasm. Dr Lam said, referring to the 5-millimetre electrode S separation distance, that it is difficult to sustain the electric discharge as S the human subject may move away from the initial contact with the T T electrode easily and, therefore, not result in neuromuscular incapacitation. U U V V  -6- A A B B Records of interview C C 20. D1 said in these interviews that the electric arc lighters were D D all bought by D2. She had no idea that the selling of these lighters would E be an offence. She said D2 demonstrated to her how to operate these E electric arc lighters. She had no idea of the energy output of these lighters. F F She was also asked to sell them at $398. G G 21. D2 admitted in the interview that he had bought the electric H H arc lighters from mainland. They were later delivered to Hong Kong. D2 I said he knew electric current would be generated when the operating switch I was pressed, but he did not know the electricity output of these electric arc J J lighters. He said he had read the instructions manual. K K 22. He said he was told by the seller of these lighters that if one L L continuously pressed the switch of the lighters for 15 seconds the circuit M would be cut. He was also told that the electric current required to charge M the lighter is small and the same is akin to that of a mobile phone. He was N N also told that it was absolutely safe. O O Exhibit evaluation reports P P Q 23. Mr Tang Kwok Ming (“PW6”) had been the assistant police Q telecommunication inspector since 1 May 1989. Since 2 March 2015, he R R was posted to the Communication Branch Operations and Support Service S Division, Electric System Support Section. The same was engaged by S police to perform technical tests and to prepare technical reports on these T T U U V V  -7- A A B B suspected stunning devices. These devices under tests were called “EUT”, C exhibit under test. C D D 24. As a result of the tests on Exhibit P1 (EUT1), two exhibit E evaluation reports were prepared, dated 18 June 2015 and 24 January 2017 E by PW6 and endorsed by Mr Chan Tak Kwong (“PW7”), Exhibits P24 and F F P25. As a result of the test on Exhibit P2 (EUT8), exhibit evaluation G reports were similarly produced by PW6 and endorsed by PW7, Exhibit G P26. As for the rest 24 electric arc lighters, similar tests were performed H H and two exhibit evaluation reports were prepared by PW6 and endorsed by I PW7, Exhibit P27 and P28. I J J 25. Exhibit P24 and P25 are both exhibit evaluation reports on K Exhibit P1 (EUT1) between 10 June 2015 and 16 June 2015. Except for K the date of these reports, the contents are the same. L L 26. In summary, it says that Exhibit P1 was capable of generating M M electric arc across the electrodes. The electrodes of the EUT were N N connected to resistor load or resistance close to that of a human being. The O peak-to-peak pulsating voltage generated from EUT across resistor load O was measured at 114,486 volts. The EUT was capable of generating P P 59,055 high voltage pulses continuously in 3 seconds duration. With the Q above measurement results, it was said in the report that the electrical Q characteristic of the EUT was similar to that of a stunning device. R R S 27. The separation between the two electrodes in Exhibit P1 are 5 S millimetres apart. There is a protective covering of Exhibit P1. When one T T opened the protective covering of Exhibit P1 and a button was pressed, U U V V  -8- A A B B Exhibit P1 was capable of generating an electric arc across the electrodes C and a sparking sound was heard. The report says that the evaluation test C aims to investigate the electrical characteristic of the EUT output voltage. D D There are four measurements in the evaluation test, namely measurement E of peak-to-peak pulsating output voltage, pulse duration, pulse repetition E interval and the number of pulses generated in 3 seconds. F F G 28. To observe the output voltage of the EUT, a digital G oscilloscope with a high voltage probe was used. The measurement was H H done by using the Potential Divider Resistor Network, which is a tailor- I made resistor network consisting of ten 200Ω resistors and two 1Ω resistors I connected in series. The total resistance of the Resistor Network is around J J 2kΩ which is similar to the total body resistance of human being. To K ensure accurate calculations of measurements, the resistance of the K Resistor Network is calibrated regularly and the value would be recorded L L in an evaluation report and the exhibit evaluation report shows the detailed M equipment set up for the measurement. M N N 29. The evaluation test measured the peak-to-peak pulsating O output voltage by discharging the EUT through the Potential Divider O Resistor Network. The peak-to-peak voltage across the resistor R2Ω using P P the oscilloscope was measured and recorded 10 times in total. The actual Q pulsating output voltage of the EUT was obtained by multiplying the Q measurement results with the resistor ratio of the Potential Divider Resistor R R Network for each measurement. The average pulsating output voltage of S the EUT was then obtained by calculation from the results. S T T U U V V  -9- A A B B 30. The one pulse waveform diagram from the oscilloscope was C captured and the diagram is attached as Annex B of the evaluation report. C The pulse duration and pulse repetition interval was measured by D D discharging the EUT through the Potential Divider Resistor Network. The E pulse waveform was then monitored using the oscilloscope. The pulse E duration and pulse repetition interval from the waveform diagram was then F F measured and recorded. The captured output waveform diagram showed G the pulse duration and the pulse repetition interval. The diagrams are G attached as Annex C and Annex D in the evaluation report. H H I 31. The number of pulses generated in 3 seconds, discharging the I EUT through the Potential Divider Resistor Network for 3 seconds was J J also measured. The waveform of the output voltage across the resistor R2Ω K was monitored using the oscilloscope. The number of pulses generated K was observed directly from the waveform if possible or obtained the result L L by calculation. The output waveform diagram was captured and the same M was shown in form of a diagram as Annex E in the evaluation report. M N N 32. The equipment set up is shown at Annex F in the form of a O drawing. It is said that the resistive characteristic of the Potential Divider O Resistor Network is measured regularly and in the report the resistor ratio P P is 899.342 and the peak-to-peak voltage Vpp (R2Ω) across the resistor R2Ω Q was measured for 10 times until the separation, with the separation between Q each time at least 30 seconds, giving the average value of Vpp (R2Ω) as R R 127.3 volts. The peak-to-peak pulsating output voltage of Exhibit P1, Vpp, S was obtained by multiplying the average value of Vpp (R2Ω) with the S resistor ratio 899.342 giving the answer as 114,486 volts. T T U U V V  - 10 - A A B B 33. In the report it said that since the number of pulses generated C is too large to be observed directly on the waveform shown, the result was C calculated. The number of pulses generated in three seconds was 59,055 D D pulses. E E 34. The procedure and methodology adopted for exhibit F evaluation reports are all the same. F G G 35. Regarding the exhibit evaluation report for Exhibit P2 H (Exhibit P26), the report says that the peak-to-peak pulsating voltage H generated from Exhibit P2 across the resistor load was measured at 87,377 I I volts and that it was capable of generating 122,950 high voltage pulses J continuously in 3 seconds interval duration. Similarly, it said that the J electrical characteristic of Exhibit P2 was similar to a stunning device. K K 36. The pulse duration of Exhibit P2 is measured at 6.8 L L nanoseconds and the pulse repetition interval was 24.4 microseconds. M M 37. As for the exhibit evaluation report for Exhibit P12 (Exhibit N N P27), although the same was capable of generating electric arc across the O electrodes, nevertheless when the electrodes were connected to the resistor O load of resistance close to human body. As in the previous equipment set P P up for testing Exhibits P1 and P2, the peak-to-peak pulsating voltage Q generated from Exhibit P12 across the resistor load was measured at Q 0 volt. It would not generate high voltage pulse continuously in 3 seconds R R interval duration. S S 38. Likewise, the exhibit evaluation report for the other 24 EUTs T T (Exhibit P28) there were similar test results as Exhibit P12. U U V V  - 11 - A A B B PW3 - Professor Carmen Poon C C 39. Professor Poon is an assistant professor in the Department of D D Surgery, Chinese University of Hong Kong. She graduated from the E Engineering Science Biomedical Programme and obtained her Master’s E degree from the collaborative programme at University of Toronto. She F F completed her PhD in electronic engineering in the Chinese University of G Hong Kong and she cofounded the Division of Biomedical Engineering G Research at the Department of Surgery. She is a senior member of the H H IEEE and has served as Administrative Committee Member and Chair of I the Technical Committee of the Wearable Sensors and Systems for the I IEEE, Engineering in Medicine and Biology Society. J J K 40. She is currently an editorial member of three international K journals. She is also the recipient of Early Career Award from two of the L L world’s largest international professional societies of biomedical M engineers, the International Federation of Medical and Biological M Engineering/ the International Academy of Medical and Biological N N Engineering, as well as the IEEE Engineering in Medicine and Biology O Society. O P P 41. She contributed to establish the Biomedical Engineering Q Program at Chinese University of Hong Kong and developed and taught Q courses on medical devices, undergraduate and graduate levels. The course R R syllabus covers the kind of medical electronic devices that measure or S apply electrical current on human body, for example, electric knives that S dissect tissues in a surgical procedure and devices that provide T T U U V V  - 12 - A A B B neuromuscular electrical stimulations. These devices share some common C principles with Conducted Energy Devices (“CED”). C D D 42. She has also led research studies as principal investigator on E blood pressure measurement devices. Sudden drop in blood pressure E (hypotension) is a known reason for syncope, a temporary loss of F F consciousness usually related to insufficient blood flow to the brain. The G underlying mechanism of syncope is related to the physiological responses G produced by CED on human subjects. H H I 43. Professor Poon has made three statements prior to the trial, I dated 25 June 2018, 28 November 2018, and 25 April 2019. She further J J made another statement dated 29 July 2019 after the defence expert on K electrical engineering raised new issues in court. She said based on the K exhibit evaluation report on Exhibit P1, the peak-to-peak pulsated voltage L L generated from Exhibit P1, measured at 114.5 kilowatts. M M 44. According to Ohm’s law, peak current on pulses when applied N N to resistance of 2,000Ω can be estimated to be 14.5 kilowatt divided by O 2,000Ω equals 57.2 amp. O P P 45. Exhibit P1 was capable of generating 59,055 high voltage Q pulses continuously in 3 seconds, each pulse in the form of a sinusoidal Q wave and with an average duration of 7.6 nanoseconds. Based on the above R R set out measurements, she approximated that Exhibit P1 is capable of S delivering a root mean square current of 3 amp. And as for Exhibit P2, the S peak-to-peak pulsating voltage generated from Exhibit P2 was measured T T at 87.4 kilowatt. U U V V  - 13 - A A B B C 46. According to Ohm’s law, peak current on pulses when applied C to resistance of 2,000 Ω can be estimated at 87.4 kilowatts, divided by D D 2,000 Ω equals 43.7 amp. Exhibit P2 was capable of generating 122,950 E high voltage pulses continuously in 3 seconds, each pulse in the form of a E sinusoidal wave and with an average duration of 6.89 nanoseconds. Based F F on the above set out measurements, she approximated Exhibit P2 as being G capable of delivering a root mean square current of 4 amp. G H H 47. CEDs such as Tasers and stun guns, she said, are high voltage I low current stimulators and can cause involuntary muscle contractions and I pain. CEDs are designed to produce electrical stimuli in the form of short J J duration (small fraction of a millisecond) repetitive pulses (5 to 30 pulses K per second) each of 50 kilowatt. K L L 48. In brief, the high voltage (analogous to pressure in a water M hose) CED is required in order to create an electric arc that bridges poor M conductors such as air gaps, clothing or dry skin (the corneum). With the N N high voltage design, even when electrodes are embedded and do not touch O the skin directly or when the skin is dry, the device can create an arc O between the probe and the skin as well as break down the dryness of the P P skin to enable the electric current to enter the body. On the other hand, she Q says, the electrical current, analogous to water flow in a hose, of CED Q determines the level of painfulness or injuries a device can bring to a R R person. The higher the current the more potential injury it brings. S S 49. There are several potential mechanisms leading to stunning T T and disabling effects of CED. These include, she said, altering the cardiac U U V V  - 14 - A A B B rhythm by stimulating the cardiac cells causing imbalance of acid-base in C the body by altering respiratory and metabolic patterns by stimulating C nerves and muscles that control breathing causing transient paralysis and D D disability by stimulating the motor neurons that control major muscles E inducing stress reactions in the human body and leading to excited delirium E through pain. F F G 50. She said delivering a certain amount of charge above a G threshold, either as a single pulse or a sequence of pules over a short period H H of time can produce one or more of these effects. With external stimulus I that accumulates charges over the threshold in less than one second the I heart can be triggered to pump a different rhythm. This can lead to J J disruptive regular blood flow patterns and dizziness. During extreme heat, K it can even result in reticular fibrillation and death. Depending on the K location where the CED is applied, one or more of those phenomenon can L L be triggered. Some of these phenomena are inter-related and they can work M together to lead to ultimate stunning and disabled effect. M N N 51. The current or delivered charge is critical for determining the O effect of CED. Human subject reported pain on average when brief high O voltage pulses at 0.5 µH were delivered to the forearms. Most subjects P P found that pain is intolerable at 1 µH. When a commonly used stun gun Q by the armed forces, namely Taser X26, is applied to the human volunteer, Q a charge of 100 µH per pulse was recorded. R R S 52. The amount of charge is comparable to a defibrillator which S is to apply transthoracic electrical impulses for a cardiac capture for T T resuscitation. Since the safety of CED remains a topic of debate there is U U V V  - 15 - A A B B limited amount of human research studies conducted under controlled C experiments. She says most of the knowledge on the effects of CEDs is C based on Taser X26 which delivers currents in the form of 15 to 19 pulses D D each and the duration about 150 microseconds. The average current is E approximated to be 2 amp. E F F 53. She says in a recent study that the probe spread is also a G determining factor for the incapacitation effect of CED and severe G incapacitation is achieved when probe distance is separated by at least 12 H H inches. Nevertheless, the same study presents a scenario where the I Taser X26 was applied in the lateral upper extremity capture during back I exposure. J J 54. Level of incapacitation did not change much for the probe K K separation distance varying from 4 inches to 12 inches. This suggests, L therefore, that, she says, that the stunning or disabling effect of CED highly L depends on whether the device is actually applied to a person, rather than M M just probe separation distance. N N O 55. Since the body, she says, is a heterogenous model, one cannot O assume current travels only along the shortest physical distance between P P the two electrodes of a CED. Once the voltage is high enough to allow Q current to enter the human body, there are chances that the current spreads Q and stimulates the nervous system inside the body. Furthermore, this study R R was designed to test only the incapacitation effect of Taser X26 under S probe operation mode and with probe separation greater than or equal to 4 S inches. It did not address the incapacitation effect of CED in the drive-stun T T mode or with electrode separation below 4 inches. U U V V  - 16 - A A B B C 56. She says both of these exhibits were estimated to operate with C a current in the region of 3 to 4 amp range. This operation range is 1.5 to D D 2 times more than that of Taser X26 and comparable to that of electronic E devices for generating painful sensation including that of perception of E shock on human subjects and pain studies. Both of these exhibits, P1 and F F P8, require less than 1 millisecond to generate a total charge of 1 µH, a G threshold that most subjects found pain is intolerable. G H H 57. The electrode separation in these two exhibits were both I 5 millimetres which is similar to some of the neuromuscular implants, I bearing in mind also that some of the electrical stimulators for vagal nerves J J and baroreceptors in the carotid region only required the two electrodes to K be separated by a millimetre range. K L 58. Given the specification of both Exhibits P1 and P2, if either L of them were applied to sensitive areas such as chest cavity and spine, both M M of them could alter heart rhythms, cause severe pain, disrupt blood flow to N N the brain and stimulate motor neurons resulting in a stunning or disabling O effect on the subject. O P P 59. The high power of both devices can also damage tissues and Q cause burn marks around the local area where the electrodes were applied. Q She, therefore, concluded that both Exhibits P1 and P2 are considered R R portable devices which are designed and adapted to stun and disable a S person by administering an electric shock applied with or without direct S contact with that person as stipulated in section 2 of the Firearms and T T Ammunition Ordinance. U U V V  - 17 - A A B B C 60. In reply to the report by the electrical engineer expert from the C defence, Mr K W Cheng, dated 5 December 2018, Professor Poon D D disagrees with what Mr Cheng said under section 5.1 and 5.2 of his report E on human impedance. She says, unlike what Mr Cheng says, electric E excitation on cells have been studied for decades. She quoted pioneer F F Nobel Prize work, the Hodgkin–Huxley Model, by doctors Alan Lloyd G Hodgkin and Andrew Fielding Huxley. G H H 61. She says that, regarding figure 5.2 in Cheng’s report, she says I human cells, including neurons and cardiomyocytes can be described by I this model. Studies of high voltage electric excitation on human body are J J few because they are generally thought to be dangerous and would cause K pain on human subjects. These studies are only ethically justified if the K protocol is carefully designed and brings new knowledge to the field. L L 62. Figure 5.2 is the model commonly used in studying electrical M M shock a person may potentially face at home or at work. To complete this N N circuit in this situation, it is always assumed the current enters the body O from one limb and exits from the other. O P P 63. In the case of EUTs, the circuit loop and the resulting Q impedance/current highly depends on the specific body location where the Q EUTs were applied. It is highly likely that there are pathways inside the R R human body when the resistances are smaller than the skin impedance. The S current would travel along these pathways rather than just on the skin. S Therefore, she does not agree to the comment that where T T U U V V  - 18 - A A B B “…the electrode (separation) is around 0.5 cm, therefore the impedance is C only skin impedance.” C D D 64. She says Figures 5.3 and 5.4 of the same report by Mr Cheng E are selected from quoted reference, “Effects of current on human beings E and livestock.” Both references clearly showed that body impedance F F drastically reduced with voltage. Figure 5.4 further shows that at 250 volts, G the skin breaks down. This is in agreement with common understanding G that skin breakdown voltage is below 500 volts and voltage above this H H threshold will cause skin to turn from an insulator into a conductor. Since I the EUTs in this case have peak-to-peak voltage in the region of 80,000 to I 110,000 volts range, no doubt the EUTs can cause skin to breakdown and J J the current entering the human body to excite the cells inside. K K 65. She says the absolute values of “Total body impedance” in L L Figure 5.3 and 5.4 are not a good reference for modelling the human body M in our case. She says these figures discuss impedance from the hand-to- M hand and hand-to-feet pathways, used mainly for electric safety at home N N and at work and this should not be confused with our present situation. O Since the electrode separation is small (in the “mm” and “cm” range), both O EUTs can be conveniently applied to specific targeted areas of the subject. P P The human body impedance for small electrode separation can be much Q lower than that shown in the Figures 5.3 and 5.4. Q R R 66. For comparison, electrical surgical knives use a load of 200Ω S and 800Ω to report their specification by bipolar and monopolar electrodes S respectively. The Canadian report used peak voltage divided by resistor T T load of 600Ω to estimate peak current from over 200 conducted energy U U V V  - 19 - A A B B devices (Taser X26). A stimulator in the carotid region also uses 600Ω to C estimate the peak current from peak voltage. If 600Ω were used instead of C 2,000Ω as the model in this case, the estimated current would be at least D D three times larger. Therefore, to conclude, the 2,000Ω model used in her E report is already considered a safe margin to account for possible E measurement and modelling errors. F F G 67. In relation to the high frequency human impedance, she says G that the Figure 5.4 shows that the total body impedance drops with H H frequency and it is below the 1,000Ω for frequencies above 5,000 hertz. I For nanosecond pulses delivered in the EUTs, frequencies are in the I megahertz range, many orders of magnitude above 5,000 hertz. If 1,000Ω J J is used as the model instead of 2,000Ω, the estimated current would be K doubled. K L 68. She also says that when the defendant expert claimed that the L only real current measurements that has been reported in the literature can M M 1 be referred to in reference [2] , she has a number of concerns in the quoted N N study [2] for reasons: O O (a) the applied stimulation was a 10 V step voltage, ie a P P low DC voltage that has no common specifications Q compared to EUTs in this case; Q R R (b) no discussion was given regarding where the S stimulation was applied; S T T 1 K S Wong, L S Chan, M L Suen, K W E Cheng, “Intelligent Switch and Smart Energy Storage for Smart City Development”, IET APSCOM International Conference, 11-15 Nov 2018, Hong Kong, pp.128. U U V V  - 20 - A A B B C (c) no discussion was given regarding the repeatability of C the measurement and the detailed study design; D D E (d) no discussion was given regarding the number of E subjects recruited for the study; and F F G (e) no discussion was given regarding whether ethics G approval or informed consent has been obtained before H H the study. I I 69. The study [2] is, therefore, not applicable and irrelevant to the J J question whether the EUTs in this case should be considered as “portable K device which is designed or adapted to stun or disable a person by means K of electric shock applied with or without direct contact with that person.” L L M 70. Although, human impedance is not a pure resistance, it is a M relevant and appropriate model to decide whether human cells can be N N excited at a specific current threshold. The value of 2,000Ω is already a O conservative estimate of the human body in evaluating the EUTs. O P P 71. She said the sine wave assumption gives a 30% reduction in Q the current estimated from the peak-to-peak voltage. Therefore, it is found Q at the present moment the most suitable model for estimating current of the R R device was as stated in the conclusions she made in the previous statement S dated 25 June 2018. S T T U U V V  - 21 - A A B B 72. As for Mr Cheng’s comment that, “Taser X26 is a very high- C powered device, whereas the EUT1 and EUT8 are very small power.” C Professor Poon does not agree. She says that Professor Cheng did not take D D into account the fact that both EUTs in this case could produce trains of E pulses in a very short period of time. E F F 73. The frequencies of pulses of both EUTS are much higher than G those of Taser X26 which is in the millisecond and second range. As a G result, both EUTs were estimated to have higher current. Power is defined H H by voltage x current, or voltage2 / resistance. When both the voltage and I current of the EUTs are comparable or greater than those of the Taser X26, I the power of the EUTs are obviously comparable or greater than Taser J J X26. K K 74. Turning to the comment to her report in Mr Cheng’s report, L L section 6.2, Professor Poon says that temporal summation of electrical M pulse trains is commonly used model in excitation of neuron cells. M Although the time range varies from milliseconds to seconds for different N N types of nerve fibres and cells, these ranges have been considered in her O reports dated 25 June and 28 November 2018. Studies in microbiology use O nanosecond and electrical pulses to increase the permeability of the cell P P membrane indicating that it is possible to open up the impermeable cell Q membrane to alternate ion influx or out flux using nanosecond pulses. Q R R 75. She does not agree with the comment that one should use the S net charge to determine pain sensation. She says it is well known that S human being is very sensitive to AC current and in some cases, a higher T T U U V V  - 22 - A A B B threshold is required for a human to perceive DC current compared to AC C current. Both DC and AC current can cause electrical shock. C D 76. Moreover, she says that the defendant expert calculated the D net charge of a single pulse on both EUTs and concluded it is very small. E E She does not agree with using this sort of calculation to benchmark the F EUTs with Taser. F G G 77. For Taser X26, each pulse has around 100 to 150 microsecond H duration but any two pulses are separated by around 50 to 60 milliseconds. H It is, therefore, reasonable to calculate charge per pulse for Taser X26. On I I the other hand, to operate the EUTs in a real life operation, a single simple J click of the button on both EUTs is able to generate a train of pulses (rather J than a single pulse) because human operator would not be able to control K K the device in a nanosecond time frame. Therefore, it is reasonable to L consider the temporal summation effect of the train of pulses as in her L report dated 28 November 2018. M M N N 78. Again, she reiterated, given the heterogeneity of the human O body, infinite number of possible designs of CED and the potential injury O a CED can bring to a human subject, reasonable assumptions has to be P P made to approximate the current and to compare a EUT with other CEDs Q and other medical devices. Voltage and current can be divided into AC Q and DC components. R R S 79. In her report dated 25 June and 28 November 2018, she has S made the following assumptions as to the estimated current of the EUTs: T T U U V V  - 23 - A A B B (1) RMSDC is negligible; C C (2) waveform is close to a sine wave; D D E (3) resistance value is relatively high (2,000 Ω). E F F 80. These assumptions have reduced the possible current by a G factor of at least two to three times. Therefore, it is reasonable, she said, G to conclude that both EUT1 and EUT8, ie Exhibit P1 and P2, should be H H considered as portable devices which are designed or adapted to stun or I disable a person by means of electric shock applied either with or without I direct contact with that person. J J K 81. In response to Mr Cheng’s argument that a skin effect on the K electronics components can be a factor affecting the measurement accuracy L L of the EUTs, and subsequently affect the conclusion whether or not the M EUTs are stunning devices. Professor Poon replies that skin effect is the M tendency of an alternating electric current (AC) to become distributed N N within a conductor such that the current density is largest near the surface O of the conductor and decreases with greater depths in the conductor. The O electric current flows mainly between the outer surface and a level called P P the skin depth. The skin effect causes the effective resistance of the Q conductor to increase and high frequencies where the skin depth is smaller. Q R R 82. For the test set-up, skin effect, she says, is most prominent on S the conductive wires. At higher frequencies in the megahertz range, the S resistance of the wires can no longer be considered negligible. By T T U U V V  - 24 - A A B B examining the figures of the circuit box, wires are considerably longer in C the following segments: C D D (1) between the external electrode 1 of the EUT and the E first test point (TP1); E F F (2) between the external electrode 2 of the EUT and the G second test point (TP2); G H H (3) between the TP1 and the probe of the oscilloscope; and I I (4) between the TP2 and the ground of the probe. J J K 83. Skin effect on the wires in all these four segments, she says, K would result in underestimating resistance total of the test circuit and/or the L L measured peak-to-peak voltage between TP1 and TP2. On the other hand M the two 1Ω resistors are tightly connected to each other as well as TP1 and M TP2. There is no evidence that R2Ω has been underestimated due to skin N N effect. Therefore, skin effect on the electronics components of test circuits O in this case will only reduce the Resistor Ratio and the measured peak-to- O peak pulsating output voltage of the EUTs which is to the benefit of the P P defendant. Q Q 84. As for the parasitic effects of the electronic components used R R in the test setup, Professor Cheng is saying that there are parasitic S impedance in the resistors R1-12, as well as in the measurement probe and S the oscilloscope. Professor Poon agreed with him in this regard. She T T further points out that since the arrangement and the exact values of these U U V V  - 25 - A A B B parasitic impedences are unknown, to postulate the effects and draw C meaningful conclusions are difficult. For example, to consider parasitic C impedences of a single resistor, one has to consider its resistance, D D inductance and capacitance. E E 85. These components can either be connected in series, in F F parallel or partly in series and partly in parallel. With different postulated G arrangement, the resulting frequency responses would be different. If these G factors were to be considered, the measured value might not be directly H H comparable to other existing CEDs which normally use only a single I resistance value to report their specifications. Moreover, since the output I voltage and frequency of an exhibit is unknown before the test, it is J J impossible and also unfair to tune the test circuit for each individual EUT. K K 86. As for Mr Cheng’s argument that due to the parasitic L L capacitance and inductance of the R2Ω resistor, the test circuit forms a M harmonic resonance oscillator for current and that even though the two M EUTs in this case have very unique frequency, 123 megahertz and 147 N N megahertz, this could be due to the test circuit having multiple resonance O peaks that amplify the two EUTs and the respective frequencies. O P P 87. Professor Poon noted that the test circuit is a relatively simple Q circuit, where across the measurement points TP1 and TP2, there can only Q be one effective RLC circuit. Therefore, there is no evidence, she says, R R that it can oscillate at multiple resonance frequencies and generate S pulsating voltage of different frequencies during the separate testing of S EUT1 and EUT8. T T U U V V  - 26 - A A B B 88. Mr Cheng argued that the measurements could be as a result C of noise being picked up by the test set up, rather than from the EUTs. C Different noise sources have been proposed, including: D D E (a) power lines; E F F (b) existence of motors or vibrating objects operating in the G vicinity of the test site; and G H H (c) wireless electromagnetic interference. I I 89. Professor Poon responded that since the measured signals J J were not in the frequency range of the standard electrical voltage in Hong K Kong, ie 50 hertz and the tests were conducted in a quiet and isolated room, K the first two possible noise sources can be excluded. Further, the measured L L frequency of the EUT1, which is 147 megahertz, was in the frequency band M of 146 to 148 megahertz, which is the frequency band allocated for land M mobile and reserved for government use only. The measured frequency of N N the EUT8, which is 132 megahertz, falls in the frequency band of 117.975 O to 137 megahertz, which is the frequency band allocated for aeronautical O mobile and 93 per cent of its frequency channels are vacant. P P Q 90. She said that the police have already reduced the possible Q effect of electromagnetic interference during testing. She further opines R R that as measured in a report dated 25 April 2019, given the heterogeneity S of the human body, infinite number of possible design of CED and the S potential injury a CED can bring to a human, reasonable assumptions are T T U U V V  - 27 - A A B B necessary to approximate the current and to compare EUTs with other C common CEDs and/or relevant medical devices. C D D 91. She mentioned after considering the exhibit evaluation reports E of the two exhibits, she confirmed and reiterated her conclusion in the E previous reports that these two exhibits, P1 and P2, should be considered F F as portable devices which are designed and adapted to stun or disable a G person by means of electric shock applied either with or without direct G contact with that person. H H I 92. Professor Poon further is of the view that the view taken by I Dr Ng, PW4, and Dr Chiao, PW5, on the issue of electrode separation that J J the subject devices could not produce sufficient energy was K unsubstantiated. She criticised them for not mentioning whether these K devices could cause fainting. She added that it is practically possible to L L apply the electrodes to vital organs of the victim. It is practically possible M for the assailant to apply the electrodes to vital organs of the victim such M as the neck for a prolonged period of time. N N O 93. Further, Professor Poon noted that these doctors relied on the O study of taser guns on human subjects. These studies suggested a wider P P electrode separation for effective stunning. Professor Poon addressed on Q the limitations of the study report such as that the studies have not covered Q a probe separation of less than 4 inches, that these studies concerned lean R R on the disability of the test subjects but not on the stunning effect which S are the issues in this case. The test subjects have been trained and have S heavy body build. The study avoids dangerous locations such as midline T T or cross-midline of the test subjects, ie, the probes remain on the one side U U V V  - 28 - A A B B of the test subjects. The study also avoids testing on locations such as the C chest and the neck. C D D 94. PW3, Professor Poon, says that both the parasitic inductance E and capacitance is negligible in the present case as the circuit is a simple E one and the wires are short. PW3, noting that PW7 had considered parasitic F F inductance, added that PW7 had not considered capacitance and other G arrangements, that is how different electronic components in the circuit G was arranged and she concluded that PW7 had leaned particularly to one H H side in terms of liability of the circuit in the calculation. I I 95. She said that the final result could go up or down depending J J on whether the circuit was set up in series or in parallel and she claimed in K her report, Exhibit P33, that, “The test circuit is a relatively simple circuit K where cross measurements points of TP1 and TP2, there can only be one L L effective RLC and there is no evidence that it can oscillate at multiple M resonant frequencies and general pulsating voltages of different M frequencies during the separate testings of EUT1 and EUT8.” N N O 96. She further stated that had there been resonance, she would O have seen it on the oscilloscope and that the wave form grew bigger and P P bigger. She was not concerned about the noise challenge by Professor Q Cheng as said previously. Apart from the noise, she also stated that the test Q set-up was enclosed in an aluminium box of non-negligible thickness. As R R indicated, the precautions have been taken by the police to reduce the S possible effects of EMI during testing. S T T U U V V  - 29 - A A B B PW4 - Dr Ng Chung Ki C C 97. Dr Ng is a Senior Medical and Health Officer and a Senior D D Forensic Pathologist. He had prepared a report dated 10 July 2015, Exhibit E P20, regarding the effect of Exhibit P1 on humans. He was tendered for E cross-examination at the request of the defendant. F F G 98. PW4 confirmed that there was a longstanding practice for the G police to hand over exhibit evaluation reports in relation to stunning H H devices to them. PW4 said it is his first time to testify in court concerning I a suspected stunning device. He admitted he is not an expert in electrical I engineering. J J K 99. He could not be sure whether Exhibit P1 is capable to stun or K disable a person but he concluded from the materials that he had that there L L is a possibility that it could do so. M M 100. He explained that the peak-to-peak voltage is very high N N because the amplitude of the peak is very high, but as for current, because O it is a long period of time between each of the pulses produced by Exhibit O P1 and although Exhibit P1 voltage is high, the total current that is passed P P through is, in fact, low. He says that as the electric arc lighter, Exhibit P1, Q was not designed as a stun gun with a U-Guard and a protective cover to Q avoid the electrodes from contacting another person, he is of the view that R R the likelihood of the Exhibit P1 being able to stun or disable a person is S very low. S T T U U V V  - 30 - A A B B 101. He also stated that there are many papers that stipulate the C greater the probe spread, the greater the chance of causing incapacitation C and confirmed that in the smaller probe spread, the possibility of causing D D incapacitation becomes less likely and agreed that a probe spread of 5 E millimetre is a very short distance and that he has never read any paper on E experiments on devices with a five millimetre probe spread. He says he F F could not, therefore, conclude whether, in fact, definitely whether Exhibit G P1 could stun a person. G H PW5- Dr Chiao Wing Fu H I I 102. Likewise, Dr Chiao is a Senior Medical and Health Officer J and a Forensic Pathologist in Hong Kong. Again, he had prepared a report J dated 22 May 2017 concerning the six electric arc lighters, not any of the K K seized exhibits in this case, and their effect on human, Exhibit 21. Again, L he was tendered for cross-examination by the defence. L M M 103. He says that the area of electrical separation distance and N N current flow in the human body is an area between biomedical engineering O and forensic pathology. He explained that while current is an area in O medical engineering, effect on human he believed would be in the area of P P forensic pathology, and as an expert, he has the expertise. Q Q 104. PW5 was the author of the PowerPoint issued by Medical and R Health Department, Exhibit D2. R S S 105. PW5 maintained that stun guns which deliver electrical pulses T by contact of the skin only are unlikely to incapacitate a person. They can T only induce severe pain and not even cause dizziness. He is of the opinion U U V V  - 31 - A A B B to compare the drive-stun mode of Taser X26 with the electric arc lighters C with a 5 millimetre electrode spread is most appropriate. He agreed that C the probe mode of Taser X26 is completely different from electric arc D D lighters and is not comparable. He is of the opinion that without the dart E probe, it would be very difficult for current to penetrate the skin. He said E that the design of the subject electric arc lighter in this case has the F F protective cover and their electrodes are protected by the U-Guard. In G addition, the gap between the electrodes are so small that the chance that G one could easily apply current on another is very low. He says if one grabs H H a person by the neck, and attempts to apply the electric arc lighter on his I aorta, PW5 opines that it would be only a contact with the skin and the I current would not penetrate any tissue. J J 106. Regarding Exhibit D6, PW5 concurs with the author’s K K illustration observation that the skin at the site of the electrode immediately L following the discharge of the drive-stun conducted electrical weapon L (CEW) displays a widened U-shape indentation in the epidermis. M M N N 107. There is no full thickness breach of the epidermis, but there is O a loss of stratum corneum at the electrode contact site. The dermis lacks O hemorrhage, thrombosis, inflammation, or other collagen change. P P 108. He had stated, comparing to the drive-stun mode of the Taser Q Q X26, it would be even harder for the electric arc lighters to breach the R epidermis. PW5 definitely concluded that in his opinion that the electric R arc lighters in his case could not stun or disable a person. S S T T U U V V  - 32 - A A B B PW6 - Tang Kwok Ming C C 109. Mr Tang, Assistant Police Telecommunication Inspector, was D D the one responsible for actually performing tests on and preparing the E exhibit evaluation reports of a suspected stunning device in this case. E F F 110. In cross-examination in court about possible problems with G the resistors in the test circuit, PW6 testified that had there been any G problem with the resistors, for instance, when the current was too high, the H H resistors would have burnt and he would have noticed a burning smell. In I these circumstances, oscilloscopes would not have been able to show any I measurement results. J J 111. PW6 said that he had not noticed any burning smell and was K K able to carry on all the 10 measurements with each EUT. PW6 stated that L he did check the resistors before the tests commenced but he would not L check the resistors each time after a measurement had been taken since the M M resistors are inside a resistors box with a cover. N N O 112. PW6 also said that there was a trimmer switch on the probe to O calibrate and optimise the square wave. He testified that he did not use the P P trimmer at all to tune or adjust the waveforms to optimise the square wave. Q He assumed that the probe was calibrated wherever the oscilloscopes were Q and that the trimmer would have been adjusted then. PW6 also testified R R that the oscilloscope had been set to a capture mode, also known as the S trigger mode. Once he placed the electrodes of the EUT at the two contact S points marked, “To external electrode 1 of the EUT,” and, “To external T T electrode 2 of the EUT,” as shown in the exhibit evaluation reports, then if U U V V  - 33 - A A B B the oscilloscope could capture any voltage, an image would be shown on C the screen automatically. C D D 113. Under cross-examination, as pointed out to PW6, the highest E and lowest peak-to-peak pulsating output voltage for Exhibit P2 was 113 E and 64 respectively and the extremity was significant. He explained that F F he was merely responsible for recording the facts. He followed procedure G and took 10 measurement pulse samples, then calculated the average G voltage output and recorded it down. It was put to PW6 that other than the H H trigger mode, there is also another mode that of the oscilloscope being the I manual mode so as to avoid the oscilloscope only automatically capturing I pulses with high voltage. PW6 confirmed that there is a manual mode but J J he did not use it. K K PW7 – Chan Tat Kwong James L L 114. Mr Chan has a Bachelor of Engineering Degree in Electrical M M Engineering and Master of Science in Management. In years 2002 to 2004, N N he was the laboratory manager of the COMMS laboratory, O Communications Branch, Information System Wing of Hong Kong Police, O which was recognised by the Hong Kong Laboratory Accreditation P P Scheme. He now handles huge electronic system projects in Hong Kong Q Police. Q 115. He says that in his witness statement date 29 April 2019 R R (Exhibit P19) that the aims of the evaluation tests are to investigate S electrical characteristics of the EUT output voltages in the measurement S readings of peak-to-peak pulsating output voltages, pulse duration, pulse T T repetition intervals and numbers of pulses generated at three seconds U U V V  - 34 - A A B B intervals were recorded. In order to avoid unstable equipment readings and C eliminate unreliable measurement results, the measurement data was C averaged for precise results. D D E 116. He says that based on the summarised observation and E obtained readings, they concluded that both Exhibit P1 and P2 were F F capable of generating electric arc electrodes. The peak-to-peak pulsating G voltage generated was respectively 114,486 volts and 87,377 volts and they G were capable of generating 59,055 and 122,950 high voltage pulses H H continuously respectively in three seconds interval duration. He said with I the above measurements that these electrical characteristics of the EUTs I were similar to a stunning device. He said that the waveform analysis and J J the measurement was not included in this evaluation. K K 117. In reply to the queries raised by Professor Cheng regarding the L L sampling rate of the equipment, he relied on Nyquist Theorem that a signal M can be measured by two times sample frequency of it. This measurement, M the sample frequency of the oscilloscope, model TDS3032B, using for N N measuring the output voltage of EUT is 2.5 gigahertz. That means that the O test equipment, oscilloscope, is capable to measure the signal frequency up O to 1.25 gigahertz in theory. In this measurement the sampling rate is higher P P than the tested signal frequency about 17 times. It is over 8 times of the Q minimum sampling requirement. Therefore, the test equipment is capable Q to measure the frequency of the EUTs. R R S 118. Therefore, Professor Cheng’s query about the equipment S accuracy, PW7 said in his report that based on the record the test T T equipment, oscilloscope model TDS3032B, was sent to Hong Kong U U V V  - 35 - A A B B Calibration Laboratory for calibration on 14 August 2014 which was about C one year before the dates of the two EUT measurements. Therefore, one C should not be concerned about the equipment accuracy. D D E 119. Referring to the query about the resistor for testing in the E measurement, he says that the 2,000Ω resistance (resistor load) for F F simulating the resistance of human skin were formed by 10 numbers of G 200Ω carbon film resistor in series connection and 2 numbers of G 10Ω carbon film resistor in series connection. These resistors were brought H H from an electronic components shop. There is no specification of this I resistor. However, the measurement record of the resistor load from I 10 July 2014 to 25 November 2015 was listed in the table enclosed in his J J report, which clearly showed the range of total resistor value from 1,978 to K 2,268Ω. It was indicated that the resistance value of the resistance divider K box (resistor load) is quite stable without any changes, even occasionally L L loading the high voltage pulsating signal. The resistor load was solely used M for measuring suspected stunning device. M N N 120. He then went on to respond to the query about the time O constant of resistor circuit and said that the resistors were soldered one by O one in series connection and formed a about 2,000 Ω value resistor load by P P a qualified technician of Hong Kong Police. Professor Cheng said the Q measured waveforms are not accurate due to the LR circuit which may Q introduce up to five nanoseconds time constant. However, he says this R R testing model for EUT evaluation is not able to obtain the exact waveform S of the high voltage signal without distortion. He said the report of the S forensic pathologist also did not highlight or emphasize the waveform of T T the EUT output signal. U U V V  - 36 - A A B B C 121. PW7, in further reply to the issues challenge put forward by C Professor Cheng during trial, further prepared another report dated 29 July D D 2019 in reply. He said the resistance box in question had tested frequencies E of different stun devices covering a wide range of frequency from 7 E megahertz to 200 megahertz. And there seems to be no obvious resonant F F frequency observed. He believes that the waveforms shown in the G oscilloscopes were not caused by the resonance of the resistor network but G the generated signal from the EUT. H H I 122. He further added that a physical characteristic of carbon film I resistor is stable. He also agreed that the heat dissipation is lower and the J J thermal effect is also very small. Therefore, the resistance values of K resistors, R1 to R12, should not change due to the high but narrow voltage K pulse of the EUTs. The inference is in line with the result of the laboratory L L regular resistor network measurements. He says that the results of M measurements showed the resistance characteristic of the resistors is stable. M Therefore, the skin effect in the resistor network he wrote in his further N N statement that according to the formula of the skin effect, for high O conductivity conductor, the skin effect can be obvious. However, for poor O conductivity material, the skin effect shall be smaller. In addition, the P P resistor carbon film is a thin graphite layer, which is already a thin skin. Q Therefore, it is reasonable to assume the skin effect in carbon film resistor Q is quite small and he said the skin effect would likely appear in the copper R R wires of the circuit. S S 123. Referring to the resistor box (Photo 1) in his statement and the T T schematic diagram of the resistance box, Figure 1 in his report, the four U U V V  - 37 - A A B B copper wires that might induce skin effect resistance R(f1), R(f2), R(f3) C and R(f4). It is noticed that both R(f3) and R(f4) resistors were not the C components of the circuit of the voltage divider and it could be considered D D that they become impedance of the probe or the oscilloscope. Comparing E to the impedance of the probe and the oscilloscope, above total 51M ohm, E the value in R(f3) and R(f4) would be very small would not cause F F significant change in the waveform. In the measured voltage across G resistors, R1 and R2 would be conservative and lower than that of the G actual voltage since voltage drop in R(f3) and R(f4) before reaching the H H probe and the oscilloscope. I I 124. Coming to the issue of parasitic inductance in the Circuit, Mr J J Chan says that in his submitted report, the measurement of EUT1 and K EUT8 were based on pure resistance model of voltage divider circuit. In K response to Professor Cheng’s query about the parasitic inductance in the L L circuit, further calculation including reasonable assumed values of M parasitic inductance into the circuit was conducted. In making the M assumption the parasitic impedance of any single resistors, R1 to R12, is N N 2.5 nH in 140 megahertz, the copper wire resistance for R(f1) plus R(f2) O caused by the stun effect under 140 megahertz is 140Ω. O P P 125. Therefore, he says if considered the effect of parasitic Q inductance into the circuit and accepting the above assumption, the Q measured values of output voltage of EUT1 and EUT8 shall be revised for R R forensic to re-evaluate the EUTs. At the end of this estimation, with S considering parasitic impedance in R1 to R12, he worked out the output S voltage of EUT1 and EUT8, that is Exhibits P1 and P2, would become T T U U V V  - 38 - A A B B 38.75 kilowatt and 56.46 kilowatt respectively. The pulse number of both C EUTs in the three seconds remained the same as submitted before. C D D 126. In court, PW7 says that he implemented the third generation E communication and power system to the police and the communication E system in the marine digital radar and video transfer. He also served as lab F F manager responsible for equipment calibration for various departments and G the lab was accredited until year 2004. G H 127. As far as the set-up of the test circuit was concerned, he said H that this was first designed by his senior colleague in collaboration with the I I pathologist and later the tests included also the three seconds functionality J test. The test procedure was used to test the suspected stun device and J would be sent to Telecommunication Department. K K L 128. In relation to the parasitic inductance/capacitance, PW7 said L this exists in all components and that the parasitic inductance and M M capacitance might compensate each other negating the overall effect. As N N for the skin effect, he said with reference to other telecommunication O system that he had worked with, he considered the effect was so minimal O and insignificant to be considered. It is also impractical and reasonable to P P assume that any such skin effect would convert unevenly to affect the Q result. He further commented that in order to produce oscillation on a Q certain frequency, that would require careful design. It would hardly occur R R by chance. S S 129. In court, he stated that after checking with the certificates of T T calibration, the oscilloscope model TDS3032B used to measure Exhibit P2 U U V V  - 39 - A A B B and the other 25 suspected stunning devices were calibrated on 14 August C 2014. When the devices were tested on 28 August 2015, it was only two C weeks after the 12 period from the last calibration. The same was D D recalibrated again with certificate as Exhibit P29(4). PW7 claimed that by E comparing the error data on the certificate of calibration one could confirm E the amount of deviation in the measurement on the oscilloscope. As for F F the oscilloscope used to test the voltage output of Exhibit P1, model TDS G 3034B, PW7 said that the same was calibrated once every 18 months. It G was calibrated 16 December 2013 and again on 5 to 6 August 2015. H H Exhibit P1 was tested on 6 June 2015 when the same was supposed to be I recalibrated. He says he confirmed that he did not have specification from I manufacturer as far as the resistors used in the test circuit is concerned or J J documentation to show that the resistors are able to perform under high K voltage situations. K L L 130. He said, however, that the resistance value was measured by M a resistance meter, almost known as multi-meter, with a voltage around 3 M to 9 volts. He agreed that by so measuring does not mean that the resistors N N were capable of functioning properly under high voltage situations of 8 O kilowatt or above. He also agreed that the frequency of the multi-meter is O completely different from that of the suspected stunning devices and he P P agreed that the resistance value of the resistors would be affected by high Q voltage and high frequency, but the change would be insignificant. Q R R 131. As for the accuracy of the probe, PW7 admitted the same had S not been calibrated. He said one could use the trimmer to tune the S waveform and optimise the square wave to ensure that the probe was T T functioning properly when used on the oscilloscope. He had mistakenly U U V V  - 40 - A A B B believed that PW6 had done the same. He admitted that he had no C knowledge of the age of the probe or from where the same was purchased C and he never inspected the probe for ageing. As for the other stunning D D devices which were able to produce electric arc but gave the final zero volt E measurement, PW7 said that is a fact and he denied any inconsistency. He E did not find it necessary to find a suitable oscilloscope for not measuring F F any voltage. PW7 admitted there were steps to analyse why the EUT were G able to generate electric arc but without any measured voltage, but he did G not perform such test. H H I 132. PW7 agreed that there are parasitic inductance effects and I resistance at high frequency which would make the resistors not just J J resistive but capacitive and inductive. He also admitted in cross- K examination that parasitic inductance and capacitance would exist at the K contact point between the probe and the resistor board, between the probe L L and the oscilloscope, in the solder used to solder the resistor to the resistor M box, between the EUTs and the contact points when testing. He admitted M he did not know the range for parasitic inductance and parasitic capacitance N N in the circuit. O O 133. Although, PW7 claimed the parasitic inductance are P P negligible, he put in a presumed value for parasitic inductance in his Q recalculation which resulted in a drop of 50 per cent roughly of the peak- Q to-peak pulsating voltage for Exhibit P1 and P2. PW7 said he tried to make R R them as close to or equal to or possibly equal to the values of R1 and R2. S When cross-examined that the value should be a larger figure, PW7 said S that he, in fact, did not know and he had no experience in measurement of T T this kind of resistance. U U V V  - 41 - A A B B C 134. Coming to the issue of oscillation and LC resonance, PW7 C says in his statement, Exhibit P32, that the tested devices are of different D D types of stun devices and they cover a wide range of frequencies and there E is no resonant frequency observed. He believed that the waveform in the E oscilloscope were not caused by the resonance of the resistor network but F F generated signal from the EUTs. G G 135. In relation to the possible EMI noise affecting the test result, H H he said that the tests were performed in a room and, although, there was no I strict protocol in place to avoid EMI when tests were conducted and there I was no measurement to confirm that there was any induced voltage in EMI J J in the resistor box. K K Defence case L L M 136. The defendant in this case elected not to give evidence. M N N DW1 - Professor Cheng O O 137. Professor K W Cheng is an expert witness in electrical P P engineering. On 5 December 2018, he prepared a report in this case Q including commenting to the exhibit evaluation report on Exhibit P1 and Q Exhibit P2, prepared by Mr Tang (PW6) and Mr Chan(PW7). He is the R R professor of the Department of Electrical Engineering of the Hong Kong S Polytechnic University. His research areas are on power electronics, S electronic circuit, converters, energy saving and renewable energy. He has T T in electrical engineering for more than 30 years. U U V V  - 42 - A A B B 138. He claims to be experienced in power circuit research and C development including high voltage, high conversion, transformer and C bioelectronics. He has developed more than 100 projects in power D D electronics and electrical engineering with over 300 publications in those E areas. He has also received awards in relation to power conversion. Recent E to his writing of the said report, he had conducted research on human F F impedance and associated protection. He has experience as an expert G witness in electrical engineering in court. G H H 139. In his report he raises doubt on the accuracy of the I measurements in the exhibit evaluation reports. He criticised the use of I oscilloscope in the exhibit evaluation report test, ie TDS3032B. In the case J J of Exhibit P2 and TDS3034B in the case of Exhibit P1. He says both K equipment are of sampling rate of 2.5 GS/s. In the former case, the K measured waveform is of 6.8 nanoseconds and the latter 7.6 nanoseconds. L L He says that oscilloscope uses interpolation to construct the waveform and M the accuracy is not confirmed because the sample rate is slow to measure M the waveform with small pulse width. He also says the equipment should N N be calibrated once every 12 months, otherwise, the accuracy of the O measurement is not confirmed. O P P 140. As for the set-up of the testing equipment, firstly, he said Q because of the high voltage measurement, the use of 10 times 200Ω Q resistors and 2 times 1Ω resistors are used to reduce the voltage to low R R enough for measurement. There are no descriptions of the accuracy and S the voltage ratings of the resistors used. He estimated that the voltage S impressed on the 200Ω resistors is 4.36 kV. He said further that there are T T very few resistors in the market that have voltage ratings of over 4 kV. U U V V  - 43 - A A B B C 141. He says that if the resistor is not of sufficient voltage rating, C the measured result is not accurate. He says most of the resistors in the D D market is only about 50 to 400V rating. Also most resistors specified at E voltage ratings at DC, and there is no information for most resistors in the E market specified with high frequency AC, especially if the frequency of F F the measurement is around 147 megahertz, estimated using 6.8 nanosecond G pulse width. If the voltage rating deviates by many times, the result of the G measurement, he says, is not reliable. H H I 142. He then goes to say that if in the electric current, there is a I parasitic effect of the circuit coil inductance. A short wire of a few J J centimetres will form inductance in the order of µH, the use of 10 resistors K of 200Ω and 2 resistors of 1Ω connected in a series would create a certain K amount of series inductance. There is no information of the resistors types L L used and also the wiring between the wires. There is no information of the M measured inductance on the set-up. M N N 143. He says that if the 12 resistors connected in a series and also O with the wires, the estimated parasitic inductance can vary from 1 µH to O 10 µH. The time constant T of the set-up is estimated to be between 0.5 P P nanoseconds to 5 nanoseconds and using this time constant to measure Q 6.8 nanosecond waveform is not accurate. Q R R 144. Professor Cheng also commented that as the output of the two S EUTs are high voltage and high frequency, there is a chance that S impedance drops at high frequency. T T U U V V  - 44 - A A B B 145. Coming to the report by Professor Poon, Professor Cheng says C it is uncertain to say human impedance is 2,000Ω and that they behave C strangely at high frequency and high voltage. He says the definition of D D 2,000Ω does not apply to around 100 megahertz frequency and 100 E kilowatt condition and that the response of the current may not be a E sinewave. Further, the rise time of the current under such condition is F F unknown. G G 146. He says further that as the voltage is AC waveform, the charge H H developed as positive and negative with positive cancelling the negative I effect and net charge is very small or approaches zero. Further, he says I parasitic effect on human subject arise time current has not been J J considered. He says that the actual charges are much smaller. As the actual K current passing through the human subject is unknown he says it is unfair K that Exhibit P1 are comparable devices to other CEDs such as stunning gun L L or Taser. M M Discussion N N O Issues O P P 147. There are three issues in this case as described by the defence; Q Q (1) whether testing method and equipment on the seized R R devices are reliable and whether they yield an S accurate result; S T T U U V V  - 45 - A A B B (2) whether Exhibits P1 and P2 are portable devices C which is designed and adapted to stun or disable a C person by means of electric shock applied either with D D or without direct contact with that person; and E E (3) whether D1 and D2 had any knowledge of the nature F F of the seized devices; namely, whether P1 and P2 are G portable devices which are designed and adapted to G stun or disable a person by means of electric shock H H applied either with or without direct contact with that I person. I J J 148. D2 is a man of clear record and due consideration regarding K his propensity to commit crime and credibility has been given. K L L 149. This court in dealing with the three issues has already M carefully considered all submissions by both parties and would not repeat M the evidence here because the same has already been set out previously. N N O Issue 1 O P P 150. This court now deals with the first issue. Q Q 151. Both Professor Poon and Professor Cheng for the defence are R experts in electrical engineering. Both of them have not taken part in the R actual evaluation tests performed on Exhibit P1 and Exhibit P2 and S S Mr James Chan and Mr Tang were responsible for these tests. T T U U V V  - 46 - A A B B 152. Mr Chan is an expert. Mr Chan has served over 20 years and C has performed and managed a lot of projects concerning high frequency C electronics. He used to be the lab manager for equipment calibration of D D various departments and the lab was an accredited one by Hong Kong E Calibration Lab, the most authoritative body up to the year 2004. E F F 153. It is noted that at this juncture that the laboratories used by G Professor Cheng at all material times was not accredited. G H 154. It is not challenged that the testing procedure had been H designed for some time in collaboration with the pathologists and revised I I to include the three seconds functionality test. Throughout the years, the J same has been employed to test these stun guns or devices. The criticism J on sampling rate has been dealt with by both Mr Chan and Professor Poon K K based on the Nyquist Theory which this court accepts. L L 155. For the calibration issue of the oscilloscope, firstly, although M M they were not punctually calibrated every 12 months, the delay is not N N substantial; secondly, from the calibration results of this oscilloscope O following the tests of Exhibit P1 and Exhibit P2 in question, they did not O show any irregularity in the error data. It is also accepted by Professor P P Cheng that Tektronix is a high quality brand for oscilloscope. Q Q 156. As for the probe, according to the prosecution witnesses, no R R apparent abnormality was observed in the waveform. There is, therefore, S no need, they say, to use the trimmer to fine tune the probe. Further, both S Mr Chan and Mr Tang did not observe any abnormality throughout the test T T U U V V  - 47 - A A B B and in the test results. There is, therefore, no evidence to suggest that the C probe had not been properly performing as it should. C D D 157. Coming to the resistors, it was submitted by the defence that E there is no specification from the manufacturer regarding the resistors E employed. Nevertheless, according to Mr Tang there is again no sign of F F abnormality noticed. Whilst the tests were performed, there is no smell or G signs of burning and sudden loss of readings. In fact, there had always G been 10 measurements during these tests and overall there is no H H abnormalities observed even in the measurement readings. All resistors I have been measured in the lab by a multi-meter. Coming to the criticism I posed by Professor Cheng, again, there is nothing from the test results and J J indeed any evidence before this court to suggest that the resistors have not K been performing as measured by the multi-meter. K L L 158. As Professor Cheng admitted there is seldom any factory M specification for any resistors based on AC conditions, it is, therefore, M impracticable for this to be expected unless, of course, there is evidence N N leading to suspicion that these resistors have not been performing as they O should under the present high voltage test situation. O P P 159. In the course of Professor Cheng giving evidence in court, he Q presented further new issues to challenge the accuracy of the test results. Q When questioned why he did not present these new issues in his report R R earlier, he explained that he had only been given the photographs of the S test circuit, Exhibit P19B, at the start of the trial. This court noted that the S set-up of the test circuit was in his report in the form of a diagram and T T though there is an absence of the photo, this court is unable to accept this U U V V  - 48 - A A B B explanation as valid for the reason that these new issues, namely, frequency C induced resistance by reason of parasitic inductance, skin effect, noise and C possible oscillation, etc, did not emerge earlier. D D E 160. Further, in cross-examination, Professor Cheng E acknowledged that invariably in any testing or calibration equipment, it F F brought into the picture those characteristics also. He also considered that G accuracy is only a relative thing and the issues is about whether the test G results can be used practically. For example, it is not in dispute that all H H parasitic inductance/capacitance existed in all components and they may I compensate each other negating the overall effect. However, he did not in I his report criticise failure in the testing procedure adopted by the J J prosecution in not having these characteristics predetermined. K K 161. Mr Chan (PW7) dealt with the new issues in his further report. L L In order to demonstrate, he has made new calculations based on certain M assumptions on the overall parasitic inductance of the circuit, the resulting M voltage was reduced by 50 per cent. N N O 162. Professor Poon maintained her criticism of this assumption of O overall parasitic inductance used by PW7 in his new calculation saying it P P is a biased one leaning in favour of an inductive circuit. She says given Q such circumstances, her conclusion on the effect of Exhibit P1 and Exhibit Q P2 on the human body are still valid and she has already provided a buffer R R in her calculation to cater for any test uncertainty. S S 163. Mr Chan did not offer actually any different explanation as to T T why he selected that particular figure. Although, the defence in cross- U U V V  - 49 - A A B B examination of Mr Chan did offer certain figures, there is no basis before C this court as to why those figures are offered. The cross-examination could C only result in the admission by Mr Chan that he is not experienced in these D D sort of high voltage measurement projects. E E 164. On the skin effect issue, the court again preferred the expert F F view of Professor Poon to that of Professor Cheng. In fact, Mr Chan shares G the same view that there is no reason why the skin effect would unevenly G converge to cause an impact to the test result and, further, as said by Mr H H Chan, any effect would be minimal and insignificant. I I 165. In fact, Professor Cheng in cross-examination agrees that J there is no special reason why the skin effect would converge only at the J 2 Ω resistors alone. K K L 166. Then coming to the oscillation issue, Mr Chan said there was L no oscillation during the test. They did not observe any resonance. He M M said that to produce oscillation on a certain frequency requires careful N N design and can hardly occur by chance. He said that the same resistance O box was used to test many devices operating from 7 megahertz to 200 O megahertz and that the circuit has multiple resonance frequencies across 7 P P to 200 megahertz is unimaginable. Professor Poon agrees that for a simple Q circuit as the one in question, it is impossible to have multiple resonant Q points as Professor Cheng suggested. R R S 167. Lastly, coming to the noise issue, Professor Poon said that the S set-up of the said circuit has also catered for such risks and again the test T T results do not suggest noise playing a part in possibly making the results U U V V  - 50 - A A B B inaccurate. This court prefers and accepts the expert opinion of Professor C Poon on the above issues to that of Professor Cheng. Her analysis is logical C and convincing and her evidence is forthcoming, even in cross- D D examination. Her evidence is totally unshaken. E E 168. This court is of the view that the report produced by Professor F Cheng on the study of wireless power transfer design for the purpose of F transfer of high energy did not, as said by the prosecution, assist the court G G on the noise issue. H H 169. Professor Cheng is a very experienced electrical engineering I I expert and this court doubts why he would have missed these new issues J from his report in the first place if these factors could really and J significantly affect the test results. As said, this court does not accept his K K explanation based on delayed submission of the photo, Exhibit P19B. L Professor Cheng has further raised concepts of proximity effects, second L order effect or matrix effect in court near the end of the trial. M M N N 170. Again, this court considers that had all these been real O challenges to the accuracy of the test results, he would have already O disclosed much earlier these elements or factors. Whilst he is an expert in P P electrical engineering, in the context of our case here, the approach of Q Professor Cheng appears to be pedantic and academic. This Court is not Q with him on the issues that he raised. They would not cast doubt on the R R accuracy of the test results of the exhibit evaluation reports. S S 171. In all, on issue 1, in spite of all the issues raised by the defence, T T the court finds that the testing method and testing equipment used in the U U V V  - 51 - A A B B tests on Exhibit P1 and Exhibit P2 is reliable and the test results accurate C for the purpose of this trial. C D D Issue 2 E E 172. Now coming to issue 2, Professor Poon is the only biomedical F F engineering expert, in my view, most suited and qualified to tell the effect G of the device when applied on humans. There are, of course, live evidence G and reports of the two forensic pathologists as well as the reports of Dr H H Lam before this court. I I 173. Professor Poon has concluded and has in cross-examination J J agreed that the functions of the EUTs in the present case are more similar K to generic stun guns and the drive-stun mode of Taser X26, rather than the K probe mode of Taser X26. Defence criticised Professor Poon for not L L mentioning the drive-stun mode throughout the first three expert reports. M Professor Poon explained that she had already taken the drive-stun mode M of Taser X26 into consideration. She claimed that in all her reports she had N N all along been discussing what would have happened to have a person when O the drive-stun mode is used. O P P 174. This court considers these criticisms unfounded. In her Q reports, Professor Poon has set out how conducted energy devices (CEDs), Q operate. She did refer to a list of references involving Taser X26. In her R R report she set out the common principles with CEDs and the underlying S mechanisms of syncope relating to physiological responses produced by S CEDs on the subject. Irrespective of the operation mode of Taser, there T T are high voltage and low current simulators. She told of potential U U V V  - 52 - A A B B mechanisms leading to the stunning and/or the disabling effect of CED C which include not just the transient paralysis and disability of stimulating C the motor neurons that control the major muscles. This is in paragraph 8 D D on her report dated 25 June 2018. E E 175. It is also said that one or more of the phenomenon can be F F triggered and they might be inter-related and can work together to lead to G the ultimate stunning and disabling effect. In fact, the mechanism as G divulged in her reports works for all CEDs irrespective of whether they are H H a stun gun, Taser gun in probe or drive-stun mode. Depending on the I electrical characteristic of each device, also depending on the location I applied on human, duration of application, etc, the effect on human would J J be different. K K 176. Professor Poon did in her report dated 28 November 2018 L L (Exhibit P16) point out that certain references she used did not address the M incapacitation effect of CED that operates in the drive-stun mode or with M the electrode separation below 4 inches. She was then referring to N N reference 5 2(see last sentence in paragraph 8). As said by Professor Poon, O studies of high voltage electric excitation on the human body are few O because they are thought to be dangerous and cause pain on human P P subjects. Q Q 177. Professor Poon was also criticised to have omitted a certain R R part of the references material when the same does not suit her. For S example, she failed to include in her report the findings by an author of a S T T 2 J Ho, D Dawes, J Miner, S Kunz, R Nelson, and J Sweeney, “Conducted electrical weapon incapacitation during a goal-directed task as a function of probe spread,” Forensic Science Medicine and Pathology, vol 8, pp 358-366, Dec 2012. U U V V  - 53 - A A B B reference that, “Electrodes 5 cm applied directly or over the vastus lateralis C muscle, a muscle in the thigh, does not inhibit voluntary function of the C muscle during stimulation or afterwards.” D D E 178. Professor Poon in court says that she does disagree that the E electrical current resulting from the drive-stun mode is localised to the F F muscles in that area. She also disagrees that the drive-stun mode does not G cause muscular incapacitation. She says that the conclusion of the author G only referred to disputation of excited delirium, which the defence H H disagrees. This conclusion appears on page 22 of the reference to under, I “Section 6 - Excited Delirium.” While the author did not qualify the I conclusion and recommendations in this section as relating solely to J J excited delirium, this court does not find Professor Poon’s disagreement to K this conclusion unreasonable. K L L 179. This court takes the view that depending on, again, the M electrical characteristic of a suspected stun device, the test results M measurements of the CED, the various factors required for consideration N N would include but not limited to, as said earlier, the location of application, O the duration of application, the length of the electrode separation. There is O nothing to prevent, in my view, a CED, even in the drive-stun mode, to P P cause stunning or incapacitation. Q Q 180. One must not forget that for the Taser research, the user should R R have always been using the Taser device in compliance with the S manufacturer’s instructions avoiding certain areas of application on human S subjects. Where in the present case this is not a concern for the issues T T before the court. In fact, as testified by Professor Poon, a lot of studies U U V V  - 54 - A A B B were done on Taser X26 and the CEDs were applied on human subjects C avoiding certain areas of the body and instructed by the manufacturers. C This research was done as people were concerned of the effects of this D D Taser and CED on human whether they would result in ventricular E fibrillation and/or death. E F F 181. The defence has not challenged the conclusion of G Professor Poon relying on, inter alia, Exhibit D3 of which Mark Kroll and G Exhibit D6 of which Mark Kroll was a co-author. Mr Kroll is an advisor H H and director of Taser International. He has failed to disclose his interests I and expertise. Exhibit D3 says that with the lack of skin penetration the I current flow is primarily through the dermis and fat layer between the J J laterals and there is no significant penetration beyond the subdermal (or K subcutaneous) fat layer. Since there is insufficient depth of current flow to K capture muscles, the drive-stun mode serves only as a compliance L L technique. He says, further, that with a controlled electrical weapon M applied directly over the human phrenic nerves that control breathing, there M is no effect. N N O 182. Exhibit D3 quoted the National Institute of Justice, a five-year O review of CEWs, and found that a risk of ventricular dysrhythmia is P P exceedingly low in the drive-stun mode of CED because the density of the Q current on the issue is much lower than in this mode. In Exhibit D6, it was Q said that the study was aimed at understanding the attenuating effect and R R estimated the residual amount of current flowing towards deeper layers of S tissue and finding the extent of region where the current density or the S electric field strength exceeded threshold known to cause ventricular T T fibrillation or to cause cardiac capture. U U V V  - 55 - A A B B C 183. The paper conducted that the fat and the anisotropic skeletal C muscle layers significantly attenuated currents delivered by Taser or CED D D operating on drive-stun mode in only 9 per cent of the total CEWs current E flow beyond the mid-point of skeletal muscle layer. Current density in E drive-stun mode did not exceed threshold for VF induction or cardiac F F capture outside the subdermal fat regions. G G 184. PW3 criticised Exhibit D3 as inconclusive and unreliable H because it is not an international journal that has gone through peer review. H It is noted that PW5 agrees with those conclusions in Exhibit D3. I I J 185. As for Exhibit D6 which has gone through a peer review, PW3 J says that the aim of the research aim is finding out whether the drive-stun K K mode would cause more serious conditions, ie ventricular fibrillation or L cardiac capture. She says that the LEM model is too simple ignoring the L existence of blood vessels cells in a simple simulation. She also says there M M are many papers which shows CEWs did cause a disruption to the heart N N rhythm which may cause dizziness. She refers to a sentence in Exhibit D6 O where it says, “The resulting sensation is often sufficiently strong to assist O law enforcement in gaining compliance from subjects.” She says that this P P sentence supports that the CEW would cause temporary incapacitation. Q Q 186. PW3 is further criticised for comparing Exhibit P1 and Exhibit R R P2 to the electrical surgical knives and neuromuscular implants to support S a view that even CEDs with electrode separation of millimetre separation S can stun or disable a person. PW3 when cross-examined explained that if T T the CED can break down the skin with high voltage they share the same U U V V  - 56 - A A B B similarities as the neuromuscular implants, including exciting the cells. C For the surgical knives, PW3 said there are some electrical knives with one C or two electrodes and the mechanism behind the electrical surgical knives D D is slightly similar to Exhibit P1 and P2. They operate at different high E frequencies which would allow her to compare voltage and current output E but their waveform or electrical knives are different and their frequencies F F might not be as high as the present exhibits. G G 187. Despite the various thorough submissions by defence counsel H H to challenge the expert view of Professor Poon, this court, considering what I is before me both from Professor Cheng and the other forensic pathologists, I accepts the explanation by Professor Poon and as well as her evidence on J J this issue. One must not forget that all tests performed on human subjects K using Taser are limited and follow the manufacturer’s instructions in K avoiding certain areas. Further, this court accepts that, as said by the L L prosecution witness, that human skin would break under, inter alia, high M voltage conditions and as such, depending on the location of application, M duration of application, this court does not doubt the conclusion of N N Professor Poon drawn on the issue. O O 188. In fact, none of the authors in these references refer to P P scenarios involving the penetration of the skin. Their views all refer to Q scenarios where there is no penetration of the skin. And, of course, Q penetration and breaking of skin depending on the depth of the flow of the R R current, the mechanism drawn from the implant is useful for the purpose S of analysing the effect of the present Exhibits P1 and P2, when used on S human and this Court agree to the expert view of Professor Poon. T T U U V V  - 57 - A A B B 189. In agreeing to the conclusion drawn by Professor Poon, of C course, the court has already considered all the opposing evidence. This C court is particular impressed by Professor Poon’s expertise both in D D electrical engineering and biomedical engineering, in particular, her E experience in the design of medical electronic devices that measure or E apply electrical current on human bodies, such as electrical knives or F F implants that provides neuromuscular electrical stimulation and the G research and investigation of blood pressure and measurement devices. G H H 190. The attacks on or the doubts attempted to be thrown by the I defence on the prosecution’s case only concentrate on the incapacitation I aspect. There is not much on this stunning aspect resulting from the J J fainting as a result of the blood pressure problem and this Court must say K that the experience and the expertise of Professor Poon obviously far K exceeded that of the other witnesses and her evidence is preferred. L L 191. In fact, both Dr Ng and Dr Chiao also agree that a biomedical M M engineering expert is the more appropriate person to comment on the N N issues. O O 192. This court, therefore, agrees with her analysis and conclusion P on this issue. P Q Q Issue 3 R R 193. Now, coming to issue 3. There is no dispute that D1 and D2 S S knew the subject devices can produce electric arc and can cause papers and T tobacco to burn. In fact, these lighters were sold as electric arc lighters. T U U V V  - 58 - A A B B 194. Professor Poon in her evidence admitted that the fact that the C lighters can produce electric arc does not mean they are stunning device, it C all depends on the actual electrical characteristics of each device. D D 195. Defence counsel submitted only two of the devices seized by E E the police satisfied the electrical characteristic of being a stunning device. F Some of the other devices seized, though can produce electrical arc, give F zero voltage readings when tested. G G H 196. It is also a fact that when one examined the lot of devices, their H design and outward appearance looked very similar and, as the police I I officers say, they could not really tell with their bare eyes which are the J ones that fit into the stunning device and which are the ones that do not. J K K 197. Clearly, tests must be performed on the devices in order to L determine whether they are, in fact, stunning. L M M 198. Both defendants elected not to give evidence in court. No N adverse inference would be drawn against them. They have, however, N previously given evidence in their cautioned interviews with the police. O O D1, as a sales lady of the shop for some time, said the subject devices were P brought by D2, her boss, and D2 did demonstrate to her how to use the P device as an electric arc lighter. She had no idea of the stunning or Q Q disabling nature of these devices. R R 199. D2 said that he was told by the one selling these devices that S the current output of the devices was similar to that of a mobile phone and S that they would not pose any danger. He produced the name card of the T T seller of these devices in the mainland. U U V V  - 59 - A A B B C 200. This court noted that when the devices, Exhibits P1 and P12, C were sold to the undercover police officers, at no time did D1 mention any D D function of the devices other than it as an electric arc lighter. Nothing was E said regarding a stunning or disabling function. Even the little tag in the E display window showing these devices only described them as electric arc F F lighter. There is no evidence before this court that these electric arc lighters G were possessed up for sale to the extra function of stunning or disabling. G There is no evidence before this court that these electric arc lighters H H possessing the extra function of stunning or disabling were sold at a price I over and above those which do not possess such function. I J J 201. In fact, when D2 used Exhibit P2 in her demonstration as to K how this device performed or operated. Later she, in fact, sold Exhibit P12 K to the undercover officer. Exhibit P12 is not a stunning device and is L L therefore different from Exhibit P2. M M 202. Now, did she intentionally sell him something different from N N what she demonstrated? There is no evidence before this court in this O respect and, therefore, it is possible that she thought the two devices were O the same. In fact, according to the evidence of D1, all the electric arc P P lighters were sold at the standard price of $398 each. There is no difference Q in price for the sale of the lighter with or without the stunning device Q function. R R S 203. Following the Court of Appeal decision in HKSAR v S Mohammed Khan Shamim, once defendants are found to be in possession T T of the subject devices, section 24(2) of the Firearms Ammunition U U V V  - 60 - A A B B Ordinance, Cap 238, imposes on them an evidential burden that they do C not know the stunning or disabling nature of the subject devices. C D D 204. The prosecution has referred me to the case of HKSAR v E Cheuk Yuet Hing, HCCC 488/2015, where the defendant was found in E possession of a stunning device, again, in the form of a lighter. But in that F F case the court rejected the defendant’s explanation that he thought the G device was just a lighter. Because the court accepted that the defendant G had in a cautioned interview told the police that the same was to be used H H for self-defence. In our case here there is no such evidence before this I court that any of the two defendants knew the devices had a function other I than that of a lighter, the nature of which is not apparent from the design J J of the device. K K 205. With their evidence in the cautioned interview, although there L L is this persuasive burden and with the observations I made regarding the M manner of sale and how these goods were displayed, both defendants, in M my view, have managed to marginally discharge their evidential burden N N and the prosecution, therefore, has failed to prove this issue 3, that these O two defendants knew of the stunning or disabling nature of the devices, O Exhibits P1 and P2. For these reasons, they are both acquitted of the P P charges and the charges are dismissed. Q Q R R S S ( K Lo ) T T District Judge U U V V