FORENSIC BIOENGINEERING
A CASE STUDY IN ELECTRICAL EMISSIONS AND CAPITAL CRIME

Abstract - This report uses elements of a recently adjudicated capital criminal case to emphasize the importance of biomedical engineering research to the workings of the criminal justice system. We relate the cutaneous signature effect of commercially available battery powered hand held electric pulse generators, commonly called "stun guns", more officially Less Than Lethal Weapons (LTLW). We cite examples of how data from this research may be of critical assistance to the criminal justice system. We present the physics and patho-physiologic effects of such LTLWs on experimental animal subjects and attempt to correlate reactions that characterize such skin responses in humans both living and dead. We discuss and compare the relationship between electrically produced signature effect and mechanically produced Triple Response, an injury phenomenon characteristic of many tissue surfaces such as skin, described by Sir Thomas Lewis[1] long before external pacers, defibrillators, stimulators, ablators, foresors, TASER's, and their progeny.

Forensic bioengineering may be thought of as a hybrid science which deals with the effects of physical phenomena and the devices which create them as related to causation and proof before the law. In this paper we consider several patho-physiologic effects on the skin produced by what are popularly, albeit incorrectly, known as "stun guns".

There now exists a large selection of pen-cell powered, hand held shock devices of simplistic electrical design capable of producing a series of less than half-joule, morphologically complex, electrical pulses at the rate of 5 to 25 per second. These pulses are most often 50 to 150 Kilovolt, 3 to 5 cycle damped transients with an energy peak in the 1000 meter radio navigation band. Finger activated bursts of these pulses of 1 to 5 seconds duration are applied by operators to the limbs and torso of human subjects. These devices have proliferated rapidly since the introduction of the semi-ballistic and operationally more complicated TASER by Cover[2] in the 1970's. During the past decade ubiquitous access, highly restrictive gun control laws, and bargain basement pricing have put several hundred thousand of these LTLW's into the hands of professionals and amateurs alike. While electronically similar to several important contemporary medical devices, LTLW's were introduced without medical claims in the early 1980's via the consumer marketplace and have thus bypassed the exhaustive governmental and scientific review accorded their medical counterparts. Currently only an occasional ad-hoc investigation or market research study is found in the easily accessible literature.

Our report deals primarily with certain cutaneous manifestations of LTLW electrical shocks, particularly the reproducibly characteristic "signature effect" on the skin. This signature effect almost always contains the three elements required of the well known Lewis Triple Response namely:

1. The rapidly formed (3-10 seconds) red spots directly beneath two or more points of energy application whose mechanism is capillary dilatation from endogenous histamine like substances released in the localized region of mild injury;

2. The "flare" or expanding reddening response due to neighboring cutaneous arteriolar dilatation from localized post synaptic antidromic nerve impulses (axon reflex);

3. The formation of wheals within the reaction sites due to increased vascular permeability in the dilated region.

A critically important requirement for development and subsidence of the Lewis Triple Response is the presence of a functional cutaneous circulation. In other words, the signature response to the typical low energy level electric current injury from a stun gun burst is arrested within seconds of the abolition of vascular perfusion. It follows that any residual signature response from application of a stun gun to a victim's body would necessarily have to have been initiated before death and not afterwards. Furthermore, post shock subsidence of the signature effect is arrested and "frozen" in place if death occurs within minutes of a well developed signature response. We believe this latter effect has not yet been reported.

The resemblance of the signature effect to the Lewis Triple Response provides a methodology for use in determination of forensic significance. We analyze this signature response in the context of bioengineering and physiology. As is typical of most forensic science this report follows the form of a careful case study rather than a controlled experimental design. The data obtained have in recent months served well the jury-based judicial process in criminal cases. Hopefully, with experimental reinforcement, they will serve as well the scientific needs of the bioengineering community.

In a previous paper[3] a method was detailed to quantify the signature effect from LTLW application to healthy human volunteers. Those results and the methods of obtaining them have been used as evidence in numerous court cases involving alleged "stun gun" injuries. The case herein required additional data to meet the legal requirements of Frye vs U.S.[4], which sets new and higher standards for technical and scientific evidence, particularly in capital matters. The decedent's body in this case had several generally circular markings on the exposed skin of the face which at autopsy were thought to be muzzle abrasions from a handgun. Law enforcement questioned this interpretation after finding the accused in possession of several stun guns.

Recalling the human studies cited above[3] a similar method of skin effect analysis was proposed using anesthetized pigs. This conferred an advantage over human experiments in that detailed surface effects could be documented photographically while permitting generous biopsy sampling of the sites for detailed histologic examination. Ten serial LTLW applications were applied to the abdominal skin of a 30 Kg domestic shoat under halothane-oxygen anesthesia. The duration of continuous pulse administration was systematically varied at dwell times from two to thirty seconds duration. Sequences of both ohmic and arcing contact with the skin was used. The LTLW probes were directly connected to the tuned output tank coil with no ohmic ground reference. In no case was any excoriation or disruption of the skin seen prior to biopsy. All three elements of the triple response were seen in all sites although wheal formation in the pig is substantially less than in humans for equal energy levels. A repeat of the above sequence under potassium chloride induced ventricular fibrillation showed no demonstrable signature effects as circulation was arrested within seconds of shock application. All runs and sites were biopsied for subsequent sectioning and staining. Parenthetically, purposeful attempts to stimulate the heart using an identical LTLW applied variously over the precordium were of no measurable effect[5].

There were several noteworthy histologic findings from the pig skin experiments. These findings were remarkably similar to the cutaneous pathology seen in super-threshold shocks as reported in Spitz & Fisher[6], and also in findings from Japan[7].

1: Nuclear streaming and vaculization: Alignment of cell nuclei along the current path through skin.

2: Epidermal thinning and wheal formation.

3: Dermal hyalinization: Coagulation of dermal collagen.

4: Vascular congestion: Dilation and engorgement of dermal capillaries with blood.

Relatively little is known about histologic changes that take place using threshold intensity electric shocks to healthy human skin. Most published data on electric shock skin changes come from industrial accidents where current densities are always much higher causing severe trauma to the skin.

All the aforementioned surface reactions of the skin to threshold electrical pulse application bear a striking resemblance to the Lewis Triple Response. As in the Lewis response, the initial reddening of the immediate epidermal focus occurs only when there is normal blood circulation to the skin. The flare reaction requires an intact and functioning local nervous system. Finally, when capillary pressure is zero the wheal reaction cannot occur. In the case of a circulation acutely arrested during signature response development, reversal of the established signature response, a process requiring minutes to hours, and in rare cases even a few days, cannot occur thus leaving a blurred but permanent record of the signature response.

If the LTLW is applied such that only the generated arc contacts the skin there is a very well defined visible signature response. If the device is applied with the probes touching the skin (ohmic contact) there is less visible signature effect. The arc tends to spread the signature response over a wider area. This is most likely due to the arc concentrating the current density at the interface between arc and skin. An increased IR drop due to the limited area of contact defines the current channel to tightly focused beginning and end points. Applying the probes to the skin broadens the current interface and the better electrical contact acts to diffuse the current density.

Little has been published in the medical or bioengineering literature on the interaction of biologic systems with high voltage low current electrical pulse devices. Stratbucker[8] reported the first animal studies involving the devices in the bioengineering literature in 1986 with further treatment of the effect on skin and cardiovascular systems in Stratbucker & Marsh [3] in 1993. Investigations to date into these effects have been ad hoc at best, since legitimate funding sources are nonexistent. The impetus for this study was from state law enforcement agencies attempting to adduce collateral and supporting proofs of guilt in a widely publicized recently adjudicated capitol case.

[1] T. Lewis, Zotterman, "Vascular reactions of the skin to electrical injury, Part VIII", J. Physiology LXII, pg 280-288, 1926-27

[2] J. H. Cover, Personal Communication 1989
See also US Patent #s 3803463,4253132

[3] R.A. Stratbucker, M.G. Marsh, "The Relative Immunity of the Skin and Cardiovascular System to the Direct Effects of High Voltage - High Frequency Component Electrical Pulses.", Proc. 15th Ann. Conf. IEEE Eng. Med. & Bio. Soc., Oct. 1993

[4] Frye vs. U.S., 293 Fed. 1013, 1923

[5] Stratbucker for Douglas County Sheriff's Dept.

[6] Spitz & Fisher (ed), "Medicolegal Investigation of Death (Guidelines for the Application of Pathology to Crime Investigation)", 3rd Ed., 1993

[7] N. Ikeda, Harada, Suzuki, "Homocidal manual strangulation and multiple stun gun injuries", Am. Jour. Forensic Med. & Path., 13v4:320-323, 1992

[8] R.A. Stratbucker, "The assessment of potential cardiac hazards in the use of hand-held electronic law enforcement devices", Proc. 8th Ann. Conf. IEEE Eng. Med. & Bio. Soc., Nov. 1986