Can Independent Analysis Save The Bacon?

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Engineers who specialize in failure analysis may investigate equipment malfunctions, structural calamities, industrial accidents, vehicular collisions or other sorts of mishaps. They then apply engineering principles in order to solve a mystery. Forensic engineering is a similar practice, where such misfortunes have legal ramifications. A forensic engineer could be trying to figure out why a building burned one week and why a plane crashed the next. Sometimes these cases make national news, while others require a small team to work in secrecy.

I’ve had the privilege of supporting many law enforcement investigations — and more than one in which the action of a law enforcement officer was the focus of the investigation. In one incident, an authority requested a confidential engineering analysis. The identities of any governments, agencies, organizations and personnel involved are purposefully undisclosed, as this writing intends to focus only on the general scope of the events and the ensuing results of the analyses. Plus … there might be some embarrassment involved!

The Incident

A “certain” government entity was experiencing an ongoing problem with landscape damage due to a large population of resident feral swine. Having a SWAT team at their disposal, the authorities granted permission for third shift personnel to hunt and dispatch any pig having the misfortune of being observed. This Hog Eradication Plan had been marginally successful for quite some time, and a number of the officers valued this as an atypical training opportunity; others expressed discomfort with the associated risks.

On an October morning at approximately 0200 hours, a 3-man patrol spotted two hogs crossing a ditch. The driver was carrying a Heckler & Koch MP5 9mm submachine gun with an integral sound suppressor and open sights. His two passengers were armed with Benelli semi-automatic12-gauge shotguns, each loaded with four rounds of 00-buckshot. All three men were carrying Glock 17 pistols, chambered in 9mm.

Reportedly, the passengers quickly exited the vehicle and each man, remaining on the paved road while firing, expended all four 12-gauge rounds at his respective target from a distance of approximately 20 yards. The shots from the first officer were well placed, and the beast expired quickly. Unfortunately, the second officer wounded his quarry, and the pig, although immobile, continued to flail and squeal.

Recognizing both members of his team now had empty magazines in their shotguns, the driver is alleged to have exited the vehicle at this time, with the intent of putting the suffering creature out of its misery. The officer fired a single round from his MP5 at the pig’s head.

A little more than half a second later, the men reportedly heard a distinct and unsettling impact in the background.
Approximately 155 yards beyond the location of the pigs — and at an angle of 13 degrees to the right of the wounded pig from the H&K shooter’s position — there was a building. On the fourth floor, which was situated approximately 65′ higher than ground level, a man was looking out of his window in response to hearing eight shotgun blasts and seeing dancing spotlights on his campus.

A second after he peered through the glass, a bullet struck the window barely a foot away from his face. If there could be any humor to this story, it lies in the irony when the man frantically called 911 to report someone was shooting at him, the dispatcher quickly and accurately conjectured it was his own emergency response team who was doing the shooting. The poor fellow had to take a week of vacation to steady his nerves after that episode.

The Investigation

After the mishap occurred, the governing authority requested the services of an independent assessment team consisting of three engineers. During the interviews, the stories among the three SWAT members were fairly consistent and there were no observable indications of deception. Nevertheless, the officers’ reports were received with skepticism by a few. Some thought the driver may have simply executed a negligent discharge, and the story of attempted euthanasia and ricochet were fabricated. The engineers conducting this investigation were fully aware more than one man’s career was at stake, and every possible aspect of this incident was thoroughly scrutinized.

Data, including dimensional and geometric measurements, were collected at the scene, and photographs were taken to document conditions. The bullet impact produced several fractures in the windowpane, but did not penetrate, and the bullet lodged in a crevice between the glass pane and the metal frame of the window. The deformed projectile was removed from the window, and its trajectory noted.

A fresh notch in an edge of the aluminum window frame matched the bullet’s path. The empty shotgun shells were located, but neither metal detectors nor bomb-sniffing dogs succeeded in locating the ejected 9mm brass case — a fact continuing to cast doubt on the incident report. Unfortunately, the bodies of the pigs had already been eliminated from the scene, and the skull of interest could not be examined.

The Bullets

The SWAT supervisor stated the officers only had two types of 9mm ammunition available in their inventory. Both types were manufactured by Federal Cartridge Company and employed jacketed hollowpoint bullets weighing either 124 or 147 grains. Interestingly, the supervisor was adamant the men were carrying the 147-grain ammo, while the driver stated he believed he was armed with the 124-grain variety in his MP5. A sample bullet from each type of cartridge was collected from the inventory for reference, and their differences were noted via laboratory examination. The “124-grain” reference bullet actually weighed 125.6 grains, while the one recovered from the window weighed 124.9 grains.

Visual Examination

The projectile in question was examined using an optical stereomicroscope. Six RH-twist riflings were observed on the full diameter of the bullet. These markings were not consistent with the geometry of riflings in factory Glock barrels; therefore, it could be affirmed the subject bullet was not fired from any of the officers’ handguns.

The bullet had been flattened against the window and the hollow cavity was collapsed. The copper jacket had separated into six symmetric segments stemming from the design-intended locations surrounding the hollow cavity. Although it was significantly deformed, the bullet appeared to be completely intact. The fore-end of the jacket on this bullet was very similar in geometry to the 124-grain exemplar, and did not resemble the 147-grain specimen. This examination, in conjunction with the weight and length measurements, indicated the subject projectile was a near 100 percent intact 124-grain bullet — not 147 grains as purported during one of the interviews.

Further inspection revealed what appeared to be smeared white metal deposited on the edge of the bullet base. This foreign metal smeared transverse to the longitudinal axis of the projectile, with directional abrasion markings on the copper jacket, indicated the bullet struck a metallic object with its base.

Since the aluminum window frame exhibited a notched edge corresponding to the bullet’s trajectory, it was suspected the smeared white metal came from the window frame. Other alien materials were observed on the bullet, including small bits of crushed glass and a piece of black foam weather-stripping. Additionally, a tiny fiber was found trapped within the collapsed hollow cavity. This fiber was noted for further analysis.

Microanalysis

The bullet was placed inside the chamber of a scanning electron microscope (SEM) for further analysis. A secondary electron (SE) detector was used to examine the topography, and a backscattered electron (BSE) detector was used to better characterize the materials involved.

The BSE detector reveals atomic contrast. Low atomic number (Z) elements appear darker than elements having a high atomic number. With the foreign metal deposit on the base of the bullet delineated, chemical analysis via energy dispersive spectroscopy (EDS) was used to identify the materials. This technique, which detects and measures the characteristic energy of X-rays liberated from the specimen by the electron beam of the SEM, indicated the jacket of the bullet was made of copper with a minor alloy addition of zinc. The foreign metal was identified as aluminum.

Needle In The Haystack

The fiber observed in the frontal cavity of the bullet was examined in the SEM. The visible portion of the fiber was approximately 1,200 microns (.050″) in length, and 54 microns (.002″) in diameter. The BSE detector provided a striking atomic contrast between the high-Z lead core of the bullet and the low-Z fiber, while also revealing another fragment of presumably organic material in the same location as the fiber.

Probing the fiber with the electron beam and generating an EDS spectrum showed the fiber consisted primarily of carbon, with minor amounts of oxygen and sulfur, in addition to trace amounts of salts. A substantial sulfur peak illustrated the fiber of interest was a natural product, such as hair, and not synthetic.

Since the fiber in the bullet was suspected to be a hair at this stage of the investigation, and the officers’ reports stated the bullet ricocheted from a hog, reference material was obtained from the head of a wild black sow, trapped for comparison.

The SEM showed the hog hairs tapered to a sharp point at the ends, and scales were observed on the outer layer. The presence of scales is inherent to hair, and scale patterns can be used to differentiate amongst various species of mammals. The hog hairs exhibited a pattern of approximately 12 scales per 100 micrometers in length. Characteristics of the reference hair sample were compared to the fiber contained within the end of the 9mm bullet recovered from the window. The dimensions, scale pattern, taper and inner cellular structure of the unknown fiber were practically identical to the features noted on the reference hog fur sample.

Consequently, it was concluded the fiber contained within the bullet cavity was indeed pig hair.

The other piece of unknown material from the subject bullet was extracted and prepared for analysis via Fourier transform infrared spectroscopy (FTIR). When infrared radiation is passed through the sample, some of it is absorbed and some of it is transmitted. A Fourier transformation applied by a computer then presents the user with a spectrum, which is essentially a molecular fingerprint of the sample. The FTIR analysis identified the material as biological tissue, and its spectrum was distinctly similar to “leather” in the FTIR reference library.

This indicated the second piece of unknown material contained in the bullet’s hollowpoint was a fragment of pigskin.

Conclusion

The evidence examined in the laboratory provided strong support to what some perceived to be an improbable story. The notch in the window frame, and the aluminum deposit and off-axis abrasions on the base of the bullet indicated the bullet was in a tumbling mode of flight. Since some sort of impulse is necessary to disrupt a stabilized flight path, a ricochet would be the only plausible explanation.

Biological materials identified as hog fur and skin were found pinched inside the deformed hollow cavity at the forward end of the bullet. The most logical way for this to happen is by collapse of the cavity upon initial contact with the hog’s skull.

Because the officers’ reports could be corroborated based on detailed independent laboratory analyses, the consequences of the event consisted of little more than three days on the beach for one officer’s loss of situational awareness.

At the beginning of this investigation, one of the SWAT officers strongly expressed his belief the independent assessment team didn’t have the technical capability to perform a ballistics analysis. Contrary to the popular stereotype, all engineers aren’t eggheads. Some of us cut our teeth on nickel-plated revolvers and have been making our own ammunition since we were teenagers.

We just might be meticulous enough to pull your butt out of a jam when no one else would spend the time to micro-analyze your situation — or have the technical acumen to solve your mystery.
By Bryan P. Tucker, PE