A Forensic Firearms Examiner's Lament

Introduction

Over the last 30 to 40 years, the connection between forensic pathologists performing autopsies on gunshot victims and forensic firearms examiners in the crime laboratory has waned to the point that in some, perhaps most locations, it has become nonexistent. This is regrettable, and if forensic pathologists want to remain informed regarding firearms and firearms-generated evidence, it is unacceptable.

Technological developments and products in the firearms and ammunition industry have undergone many changes, especially in the last 10 to 20 years. Unless the forensic pathologist is a shooting enthusiast, he or she is apt to be informationally deficient insofar as some firearms-related injuries and evidence generated during such injuries. This, of course, can result in missed evidence, erroneous findings, and a very unpleasant time on the witness stand when confronted by a prepared and knowledgeable cross-examiner.

This problem stands to be largely eliminated for those few medical examiners' facilities that are combined with the crime laboratory, but this type of organizational partnership is rare. An argument could easily be made for the employment of a firearms examiner by the medical examiner's office, particularly in jurisdictions where firearms homicides are frequent. But this solution seems highly unlikely under current economic conditions. There are several efforts that could be undertaken to minimize and reduce this disconnect. These include inviting and involving experienced firearms examiners to professional meetings of forensic pathologists with a specific request to describe and illustrate such things as new products, unusual cases, and current crime laboratory capabilities. Even simpler, invite a senior firearms examiner from the crime laboratory to participate in any autopsy that involves an atypical wound or heretofore unseen foreign bodies recovered from a gunshot wound. Since the investigation and any hope of a proper, final solution to a death by firearms starts with a thorough and reliable autopsy, the early input by a firearms examiner can be critical. I can assure the reader that firearms examiners including this writer take no pleasure in testifying that evidence that would have provided a definitive answer to the central question in a shooting death was overlooked, not recognized and not collected by the forensic pathologist. This article will provide a number of examples drawn from nearly 50 years of experience as a criminalist and forensic firearms examiner. It is hoped that these examples will stimulate a reversal and narrowing of the presently widening information gap between forensic firearms examiners and forensic pathologists.

Pseudo-Stippling

A variety of materials propelled by a bullet perforating an intermediate object near a gunshot victim can produce pseudo-stippling of the skin (1). The same is true for projectiles that are ricocheted into a victim located near the impact site. Few forensic pathologists would confuse pseudo-stippling from true stippling caused by unconsumed and partially consumed gun powder in certain intermediate and close range shootings. The general appearance, atypical sizes, and distribution of the stipples produced by propelled debris in a case of pseudo-stippling are all clear indicia of the presence of some sort of intermediate object between the gun and the victim. But the nature and identity of this “nearby” object may become the most important factor in the case as more information is developed and competing explanations of the shooting are presented. Merely reporting that “an area of pseudo-stippling was present around the entry wound with radii extending approximately 9 cm to the right and left, 5 cm above and 12 cm below the entry wound” may not be sufficient.

Let's look at glass as a relatively common intermediate object. Bullets perforating glass of any kind propel a cloud of glass fragments ranging in size from dust-sized particles to 1- to 2-mm-sized fragments. For the first one to two feet of flight, this expelled material has essentially the same velocity as the exiting bullet. The glass particles spread out in a conical fashion and lose velocity very fast; consequently, their ability to produce pseudo-stippling diminishes very rapidly (2). Consider now this hypothetical case: a driver is shot and killed by a police officer who subsequently states that he was about to be run over by the approaching car when he fired multiple shots as the car approached his position then swerved, very nearly striking him as it passed by his location. The windshield has several bullet holes in it and the driver's side window is also largely destroyed. It is uncertain if this was the consequence of a bullet strike or the subsequent crash of the vehicle. Windshields are composed of two layers of glass between which is a thin plastic layer. Side windows are made of tempered glass which effectively shatters into small square and rectangular pieces when it is broken by any means. Crime laboratories have the capability of distinguishing one sample of glass from another based on several analytical techniques (e.g., density, basic, and trace elemental composition, all of which can be accomplished on small particles of glass). The ability to identify the source of the glass that produced pseudo-stippling associated with the driver's fatal gunshot wound depends entirely on the forensic pathologist collecting and preserving a few representative particles of the glass from stipple sites. This would only take a few moments, yet it is very seldom done. The composition of these particles would be compared to control samples from the windshield and driver's side window collected by scene investigators or the crime laboratory. Consider now a subsequent courtroom scene where such autopsy samples were not collected and the trace evidence examiner from the crime lab points out the absolute critical importance of this physical evidence. The pathologist, under cross-examination, offers as his or her only defense that “I didn't know it could be important or useful”, “I never thought of doing that”, or “We don't do that at our facility.”

Now consider a ricochet situation where a bullet strikes a brick wall a few feet in front of a subject leaning against this wall. Many energetic bullets will produce a spall or crater at the impact site with the subsequent ejection of pulverized material (3). A strike into a concrete sidewalk will often do the same. Both of these situations can produce pseudo-stippling if the victim is within a few feet of the impact site. Later, one or more witnesses come forward and claim that the subject was shot while down on the sidewalk; not while leaning against the adjacent brick wall. This issue becomes important in a self-defense vs. a murder allegation. Recovery of a few particles of the material responsible for the pseudo-stippling at autopsy followed by subsequent examination at the crime laboratory would once again resolve this dispute.

The final example arises from particulate material contained in certain American shotgun shells. A granular plastic filler is included in these shells that fills the spaces between the shot to act as a buffer material. These plastic particles prevent the soft lead pellets from being deformed during the tremendous accelerative forces that occur during discharge. These plastic particles emerge intact with the shot string, quickly spread out (due to air resistance), and quickly lose velocity. But at distances out to several feet, they will produce pseudo-stippling that can, because of their fairly uniform size, look very much like stippling due to unburned powder; much more so than the previously described sources of pseudo-stippling (4). These plastic particles also spread out more rapidly than the shot pellets, consequently at relatively close distances of one, two to even three feet where the pellets may enter the body en masse, producing a single entry wound, and the stippling pattern produced by the plastic buffer around the entry wound will have markedly differing densities and diameters. There are two basic chemical versions of plastic buffer material, polyethylene and polypropylene, as well as a variety of physical forms and particle sizes, all of which relate to the brand and vintage of ammunition (5). So here again, the collection and retention of a few representative particles associated with stipple sites could be a critical factor in a case involving a shotgun death. The recovery and retention of small particles can best be accomplished with the tip of a scalpel blade followed by transferring the particles to a piece of filter paper. After careful folding of the filter paper in such a way to ensure the retention of the particles, it should be marked as to the site or area of the body from which they were recovered and then transferred to an evidence envelope with all the usual entries for case identification. A common paper envelope is preferred over air tight plastic vials or bags to prevent or minimize the putrefaction of any adhering bio-matter. The firearms examiner or trace evidence examiner in the crime laboratory will have little difficulty in differentiating and ultimately separating the plastic particles from the associated bio-matter.

Powder Particles

All modern propellants for small arms are based on nitrocellulose. Various chemical compounds are added to modify performance, but the basic chemistry remains unchanged. The physical forms that propellant manufacturers utilize to control and adjust burning rates vary considerably, and this has forensic value (6). These can vary from minute spherical particles to discshaped flakes to flat, squarish flakes. In many combinations of firearm and ammunition, some of the propellant emerges from the muzzle only partially consumed. Near the muzzle, these particles have velocities comparable to the bullet itself accounting for their ability to produce true stippling of skin in close and intermediate range gunshot wounds. The original gray graphite coating may be burned away to the extent that the particles may have a yellowish to greenish-yellow color when observed on or in the skin of a gunshot victim but the original physical form of the propellant usually survives sufficiently to be recognizable under the microscope by the crime laboratory examiner.

Consider a situation in which the investigator's first impression is a murder-suicide. The deceased husband and wife have perforating contact and near-contact gunshot wounds of their heads. A revolver is found in the husband's hand, with two fired cartridges in the cylinder. A fired Winchester cartridge is under the hammer and a fired Remington cartridge is adjacent to it. This spatial arrangement means that the Remington cartridge was fired first and the Winchester, second. Subsequent laboratory examination reveals spherical ball powder residues in the Winchester cartridge case as well as in the bore of the revolver, confirming that the Winchester cartridge was the second round to be fired. The fired Remington cartridge is found to possess residues of the disk-fake form of gunpowder. Later investigation produces an alternate explanation for these two deaths, and it is that the wife was having an affair with her husband's brother. She would not divorce her husband and was going to break off the relationship with the brother. He came to their house, ostensibly for a social visit, got in a suitable position, withdrew the previously hidden revolver, shot his brother then shot the now hysterical wife. Following this, he placed the gun in the deceased brother's hand and fled. Given a little thought, it should be apparent how the recovery of a few powder particles from the wound channel would refute one hypothesis and support the alternate hypothesis. The same scalpel-filter paper technique previously described for particles associated with pseudo-stippling will work equally well here. But in the absence of their collection during the autopsy, the determination of the true nature of this crime will likely go undetected.

Bullet Cores

With rare exception, jacketed pistol bullets contain soft lead cores. The outer copper alloy jacket allows these bullets to be driven to higher velocities than could be achieved with plain lead bullets. Higher velocity translates to flatter trajectories and increased wounding effects. Most rifle bullets are constructed in a comparable fashion. The lead cores are forced by heavy pressure into the bullet jacket during the manufacturing process. Some pistol bullets can experience core-jacket separation as they penetrate soft tissue. This is less of a problem with rifle bullets but is not unheard of. This is undesirable from the bullet manufacturer's standpoint and from a forensic standpoint. The problem that this presents for the forensic pathologist is the chance that the radioopaque lead core will be recovered as “the bullet” and not recognized as the core. This case of mistaken identity can be compounded by what might appear as rifling engravings on the bearing surface of the separated core. Seeing this, the pathologist might be satisfied that he or she has recovered the bullet, leaving the separated jacket in the decedent. But it is this jacket that will allow the brand of the bullet and its caliber to be determined by the crime laboratory, allowing identification of the responsible firearm. Careful inspection of separated lead cores at the time of autopsy will reveal either a total absence of rifling marks or only the vague impressions that have printed through the bullet jacket and into the underlying lead core. A brief, gentle washing of a separated core initially thought to be a bullet followed by a careful inspection, perhaps even with the assistance of a stereo microscope, should obviate such mistaken identity. Any reader who has not observed the distinction between a fired lead bullet and a separated lead core from a jacketed bullet would be well advised to have someone in the crime laboratory firearms unit provide a few examples as a refresher or training aid.

At this point many readers may think that the likelihood of such an error is extremely remote because the separated jacket would be visible in one or more radiograph views. This view is quickly dispelled in the case of the Winchester SilverTip product line where certain pistol and revolver bullets possess aluminum jackets. The aluminum jackets are not only given to separating from the lead cores during soft tissue penetration, but are also virtually invisible in traditional radiograph views. An awareness of this potential oversight and a little additional attention to the appearance of recovered “bullets” should save the embarrassment of a phone call from the crime laboratory firearms unit days or weeks after the autopsy inquiring as to whereabouts of the separated jacket that goes with the lead core now in their possession.

Wound Path Length

Wound path length can be of particular interest to the forensic firearms examiner, yet it is seldom described in autopsy reports associated with penetrating gunshot wounds. Path length is of critical importance for wounds produced by bullets from long distance shootings (7) and bullets that have been substantially decelerated as a result of passage through an intermediate object, a ricochet event or a previous gunshot victim. There are also mismatched combinations of ammunition and firearms that produce greatly reduced muzzle velocities for the particular bullet. An example is a 9 mm cartridge fired in a .40 Smith & Wesson (10 mm) caliber pistol. This mismatched combination will produce a muzzle velocity of about 105 meters per second (m/s) for a bullet that would normally have a muzzle velocity of approximately 350 m/s.

Celebratory gunfire with shots fired at departure angles on the order of 10° to 30° can result in bullets returning to earth 1000 to 3000 m downrange with greatly reduced, but potentially lethal velocities. Such reckless shots are to be distinguished from vertical and near-vertical discharges which result in relatively low velocity, (e.g., 45–75 m/s) free-falling and tumbling bullets (8).

By way of an example, a standard 115 grain 9 mm bullet with a typical muzzle velocity of 350 m/s with a departure angle of 10° under standard atmospheric conditions and fired over level terrain will return to earth at 1156 m with a calculated residual velocity of 90 m/s. This same bullet fired with a departure angle of 20° will travel 1485 m and have a terminal velocity of 80 m/s. Bullets of this type are only likely to produce very shallow wounds in areas of soft tissue.

Consider a case where an nondeformed 9 mm bullet strikes a victim in the back, producing a normal-appearing entry wound and only penetrates about 10 cm in soft tissue. It requires an impact velocity of about 60 m/s for a bullet of this type to breach skin and enter the underlying soft tissues (8, 9). Bernd Salziger of the BKA Laboratory in Germany prepared two plots of penetration depth vs. impact velocity for the 124 grain 9 mm NATO bullet in a recognized soft tissue simulant (10% w/w ordnance gelatin) with and without a covering of fresh 3 mm to 4 mm pigskin on the entry side of the gelatin block (10). His multiple tests shots showed a predictable, essentially linear relationship between impact velocity and penetration depth once the threshold velocity for skin perforation has been well exceeded. This threshold velocity was approximately 60 m/s. The best fit equation for shots into bare ordnance gelatin was:

P c m = 0.21 V I M P ( m / s ) − 3.2 c m

where P = penetration in centimeters, and

V_IMP = impact velocity in meters per second

The best fit equation for shots into pigskin-covered ordnance gelatin was:

P c m = 0.20 V I M P ( m / s ) − 2.3 c m

There was some slight scatter of data points above and below the best fit plot that was due to varying amounts of yaw as these bullets penetrate the ordnance gelatin. Perhaps even more interesting is the fact that the presence or absence of skin had virtually no effect on penetration depth. This can be verified by selecting an impact velocity (e.g., 150 m/s) and calculating the penetration depth from each of the equations shown above. Such calculations will produce penetration depths of 28.3 cm and 27.7 cm, respectively. This small difference of 0.6 cm is equivalent to a reduction in impact velocity of only 3 m/s yet the threshold velocity necessary to breach the 3–4 mm thick skin was approximately 60 m/s. This demonstrates something well known to many ballisticians, and this is that the threshold velocity necessary to perforate thin materials (skin, sheet metal, thin paneling) is not the same as velocity loss experienced during the perforation process (9, 11). Finally, if we apply the work of Mr. Salziger to the hypothetical example of a 12.7 cm wound path by one of these bullets, the second penetration equation yields an impact velocity of 75 m/s. This impact velocity can be used with a suitable exterior ballistics program to estimate the distance that such a bullet would have to travel under the site conditions and a given muzzle velocity to strike the victim with this residual velocity.

In the absence of any statement of penetration depth in the autopsy report, one is left with having to get an opinion from the forensic pathologist months or even years later or having another pathologist make an estimate from the available autopsy records. In summary, any effort to establish the approximate impact velocity of a particular projectile ideally starts at the time of autopsy with the pathologist's best estimate of penetration depth.

Wound Paths and the Presence or Absence of Deflection

There is considerable variation among forensic pathologists in plotting and describing a bullet's wound track. Some provide numerical estimates of azimuth and vertical angle components with the body in the normal anatomical position. Others simply give general descriptions. Still others employ probes and photography to illustrate a wound path. All seem to appreciate the uncertainty regarding the victim's actual body position at the moment the shot occurred. The various consumers of pathologists' descriptions of wound tracks frequently attach more certainty to these descriptions than they perhaps deserve or misapply them to the shooting scene and incident (e.g., a steeply downward path is taken to mean that the victim was shot from above). This, of course, is not necessarily the case.

The purpose of this section is to point out a potential source of error in assessing the course of a projectile in a gunshot victim, and that is the matter of deflection and/or deviation from the projectile's initial course. In the absence of any mention of deflection or deviation, a reading of a wound path description in an autopsy report may give the impression of a straight path. Fortunately, most pistol bullets and expanding rifle bullets that mushroom evenly do tend to follow straight paths in soft tissue and tissue simulants (12, 13). This is because their centers of gravity and centers of pressure are very close to each other and they therefore tend to mimic spherical projectiles whose wound paths are straight. Matters change dramatically with long, nonexpanding rifle bullets. These elongated bullets have aft centers of gravity whereas their centers of pressure in nose-first flight or movement is forward. Such bullets cannot remain nose-forward for long as they penetrate any “soft-solid” (gelatin, ballistic soap, muscle tissue, liver tissue, etc.). Once the nose of such a bullet tips slightly in any direction, it will yaw and depart from its original course. This may require as little as 5–7.6 cm of penetration to as much as 15.2–20.3 cm of penetration but it will happen for this type of bullet, given sufficient path length. Marked differences in wound path production typically occur between expanding (soft point, hollow point and polymer-tipped) bullets and nonexpanding full metal-jacketed bullets of the same caliber, weight and impact velocity. An expanding bullet is much more likely to follow a straight path during which it expands very rapidly producing a large temporary cavity, often leaving multiple fragments along the wound track. If the bullet is one of the many current polymer-tipped bullets, this important item of evidence will be somewhere along the wound track but it may be difficult to find. The essentially straight wound track for these expanding bullets is a consequence in the rapid shift in their centers of gravity and centers of pressure as they mushroom and become substantially shorter in length. A full metal-jacketed bullet that does not immediately fragment will deviated from its original path as soon as it yaws. The error in describing the wound path based on where such a bullet entered and where it came to rest can be as much as 20 to 30 degrees away from its origin course (3, 13). Now consider the same phenomenon with the exception that the bullet exits and we don't have the benefit of knowing much of anything regarding the bullet's design and typical behavior in a gunshot victim. Drawing a line from entry to exit on a body diagram for a gunshot wound caused by this latter type of bullet risks being in serious error.

There are two simple remedies for this potential error: 1) If a careful tracking of the bullet's course into or through a gunshot victim shows no evidence of deviation from a straight track, then note this somewhere in the autopsy report; 2) Utilize the first 7.6–15.2 cm of penetration to chart the projectile's path into the victim. This second method has long been recommended by Dr. Beat Kneubuehl, the premier wound ballistician from Switzerland and author of multiple books and articles in German and English on this subject (13, 14).

Wounds from Ricocheted Bullets

Ricocheted bullets that go on to strike a victim present special problems to the forensic pathologist. While it is well known that they often produce atypical entry wounds, this is not always the case. A ricocheted bullet is unstable in flight and is either yawing or tumbling. There are points in time and space where such a bullet returns to a nose-forward orientation. If a victim happens to be at such a location, the entry wound will appear normal. Stated another way—a normal-appearing entry wound does not rule out a ricochet.

The next matters relate to wound path and penetration depth. Ricocheted bullets not only lose some velocity during the ricochet process, but also lose velocity rapidly thereafter due to the greatly increased aerodynamic drag on their destabilized flight. The wound path length in a victim struck 100 or 200 meters downrange by such a bullet stands to be very short because of the bullet's greatly reduced velocity (15). This observation could quickly lead to an erroneous opinion of a long distance shooting. Since ricocheted bullets are already destabilized when they reach a victim, the wound paths will likely be atypical (non-linear) from beginning to end. With the exception of bullets ricochet from water, ricochet damage to the impact sides of ricocheted bullets is usually discernible to an experienced firearms examiner. In some cases it is even conspicuous and observable upon recovery at autopsy. Since the present day firearms examiner may not see such a bullet for days to weeks, if there is any suggestion or suspicion of a ricochet event at the time of autopsy, this would be one of those times to call the crime lab firearms examiner for his or her input after the bullet is recovered. Confirmation that the incident involves a ricochet should quickly change the direction of the investigation while the scene is still reasonably fresh.

Uncommon or Unconventional Projectiles

The variations and permutations in contemporary ammunition and projectiles would seem endless and ever changing even to a shooting enthusiast. Consequently there is no possibility of providing comprehensive examples in this article. Rather some selected examples will follow that seem likely to be encountered in the future, with the intention of alerting the reader to the clear possibility of encountering previously unseen and unanticipated objects in, or on gunshot victims.

Totally lead-free, disintegrating bullets are now available from at least three companies. These bullets have been developed for multiple reasons: legislation banning the use of lead bullets for environmental reasons, reduced ricochet liability, and for use by varmint hunters. Upon entering soft tissue, these bullets effectively and rapidly disintegrate leaving a fog of fine particles and small jacket fragments along a very shallow wound track. A radiographic view of a decedent shot with one of these bullets is likely to reveal nothing recognizable as a bullet or even major bullet fragment. The only fragment amid the many that is capable of being associated with the responsible firearm is the disk-shaped base of the copper jacket that once held the pressed, lead-free core material. And this is the one fragment amid the many that needs to be found. The most common core composition in these bullets is a powdered copper/tin mixture. In addition to the small particle sizes in the wound track, this material has a reduced radio opacity, and along with the numerous small copper jacket fragments.

A number of manufacturers make pistol and rifle bullets with polymer tips of various dimensions and colors. These are often dislodged during the penetration process and are somewhere along the wound track. They are not visible in radiographic views and can only be found by feel or careful visual examination of the wound track. Thoroughness and a modicum of luck will be necessary to find such small items. They all have features that relate to the brand and type of bullet and are therefore of evidentiary value. The foregoing represents just another, final reason to establish a line of communication with one or more firearms examiners in the crime lab.

Summary

I have entitled this article a lament for several reasons. The special pleasure in my early years as a criminalist working with, and drawing upon the forensic pathologist's observations and findings are essentially history today. Some of those people were shooting enthusiasts, and consequently, very firearms knowledgeable. This was a great asset that seems to be less common today.

For the most part, today's criminalists and forensic firearms examiners in the crime laboratory have little or no interaction with the forensic pathologist. Whatever the reasons or excuses given for the minimal or nonexistent exchange of information between forensic pathologist and relevant members of the crime laboratory, this situation needs to change. A course reversal is in order. I hope we are all still interested in determining what did and did not happen in a shooting incident. The status quo must change if our mutual objective is to provide the most soundly thought out opinions. Such ultimate opinions start with observable facts and measurements. The forensic pathologist must remain informed and abreast of products and developments related to firearms and firearms evidence. I have no doubt that a call to the firearms unit of the local state or city crime lab by the forensic pathologist requesting information regarding some new or unusual product would be welcomed.