“Dermal Nitrate”

The ability to determine whether an individual has fired a firearm is of great significance in the investigation of both homicides and suicides. Thus, over the years a number of tests have been developed in an attempt to fill this need. The first such test was the “paraffin test” also known as the “Dermal Nitrate” or “diphenylamine test.” In this test, the hands were coated with a layer of paraffin. After cooling, the casts were removed and treated with an acid solution of diphenylamine, a reagent used to detect nitrates and nitrites that originate from gunpowder and may be deposited on the skin after firing a weapon. A positive test was indicated by the presence of blue flecks in the paraffin. Although this test may give positive results on the hands of individuals who fired weapons, it also gives positive results on the hands of individuals who have not fired weapons because of the widespread distribution of nitrates and nitrites in our environment. The paraffin test is in fact nonspecific and is of no use scientifically. These metals, which originate from the primer of a cartridge on discharge of a weapon, are deposited on the back of the firing hand as discrete particulate matter. In revolvers these metallic particles come primarily from the cylinder-barrel gap, and in automatic pistols from the ejection port. residues. In the test a square of white cotton cloth was moistened with hydrochloric acid and then used to swab the hand. The swab was treated with triphenylmethylarsonium iodide for the detection of antimony and sodium rhodizonate for the detection of barium and lead. The limited sensitivity of this test prevented its widespread adoption. By the mid-1980s, there were three generally accepted methods of analyzing for gunshot residues: neutron activation, flameless atomic absorption spectrometry and scanning electron microscope–energy dispersive x-ray spectrometry. All three methods were based on the detection of metallic elements (principally barium, antimony, and lead) originating in primers and deposited on the back of the hand firing the weapon. Flameless Atomic Absorption Spectrometry will detect antimony, barium, and lead from the primer as well as copper vaporized from either the cartridge case or the bullet jacketing. In this method of analysis, four cotton swabs moistened with either nitric or hydrochloric acid are used to swab the palms and backs of the hands in order to recover the metallic components of the primer. A fifth swab is moistened with the acid and acts as a control. Typically, when one fires a gun and residue is deposited on the hand, it is on the back of the firing hand. Detection of primer residue on the palms of the hands, instead of on the back of the suspected firing hand, is suggestive of a defensive gesture rather than of firing a gun. It can also be due to handling a gun coated with firearms residue. In suicides with handguns, primer residue on the palm may be due to cradling the gun with this hand at the time of firing. The residue is detected more commonly on the back rather than on the palm. Occasionally, only high levels of lead are detected on the non-firing hand. It is hypothesized that the absence of antimony and barium is due to the fact that only small quantities of these elements are used in the primer and that they precipitate out inside the long barrel before they have a chance to exit in elevated levels. To correctly interpret the significance, if any, of a positive test result, one must take into account the surface area of the hand that is positive (left palm, right back, etc.); the quantity of metals deposited on the different areas, the nature of the weapon and, in self-inflicted wounds, the nature and location of the wound. The classical picture of an individual who has fired a handgun is a positive test result on the back of the firing hand and negative results on the other surfaces of the hands. If an individual, instead of firing the weapon, put their hand up in a defensive gesture, with their palm toward the weapon at the time of discharge, elevated levels of primer residue will be present on the palm and sometimes on the back of the hand. In the latter case, primer residue on the back of the hand occurs when the whole hand is engulfed in a cloud of vaporized primer residue. The levels of metal on the back of the hand will be lower than those on the palm. The difficulty with FAAS analysis is that one can never be absolutely sure that one is dealing with firearms’ residues. FAAS is a bulk, elemental analytical method involving measurement of the total quantity of metallic residues removed. One cannot distinguish the source of the metals. In addition, this technique has a high percentage of false negatives. A positive test for gunshot residues on the hands can result from handling a weapon that has been recently discharged. The residue will of course be deposited on the palms rather than the backs of the hands. The third method of analysis employs a SEM-EDX (Scanning Microscope-Energy Dispersive X-ray Spectrometery) capability. The material removed is scanned with the SEM for gunshot residue particles. These consist of discrete micrometer-sized particles, often of a characteristic shape. The Xray analysis capability is used to identify the chemical elements in each of the particles. Particles of lead-antimonybarium (Pb–Sb–Ba) and antimony-barium (Sb–Ba) composition are considered characteristic of gunshot residue while other particles, containing various other combinations of these elements, are consistent but not unique. Based on testing, it has been found that in individuals who have fired handguns, 90% of the time residue will be detectable; for rifles and shotguns, 50%.In long arms, rifles accounted for the majority of negative results. In the case of lead-free Sintox ammunition, the gunshot residue particles are spheroidal in shape, consisting mainly of titanium and zinc. Automation allows multiple unattended (automated) analyses, thereby permitting analyses of greater numbers of cases. This eliminates the labor intensive problem. If one standardizes the search parameters and the area searched on each lift, then one can express the number of gunshot reside particles per unit of area, permitting comparison of the concentration of particles on the different surfaces of the hands (palms and backs). Trace Metal Detection Technique tests depend on the detection of trace metals left on the hand as a result of handling a gun. The metal forms characteristic color complexes with a reagent sprayed on the hand. Different metals produce different colors. The pattern and color produced depend on the shape and metal content of the weapon. Whether the pattern and color are present depends on how long the weapon was held and whether the individual was sweating. As sweating increases, the pattern and color increase in prominence. In gunshot wound cases, examination of the clothing is often as important as examination of the body. The interposing of clothing between the muzzle of the gun and the skin can alter the appearance of close-range gunshot wounds of the body. Clothing can prevent soot or powder, either completely or in part, from reaching the skin as well as producing a redistribution of this powder and soot. With near-contact wounds, the clothing may absorb soot that would ordinarily be deposited on the skin as well as preventing or decreasing searing of the skin by hot gases. Complete absorption of the soot and powder by clothing can occur in what ordinarily would be called an intermediate range wound. The resultant absence of powder tattooing on the skin results in an intermediate-range wound having the appearance of a distant wound. Ball powder can readily perforate one and even two layers of cloth to produce tattooing of the underlying skin. Under unusual circumstances, it will perforate three layers. Flake powder, on the other hand, usually does not perforate even one layer of cloth unless the range is extremely close. Ball powder, because of its shape, readily perforates the weave of the cloth, producing powder tattooing of the skin. Although powder may seem to be absent on the outside of the shirt with the naked eye, use of the dissecting microscope will reveal occasional balls of powder caught in the weave of the material. individual was shot. In view of these facts, one can see why examination of the clothing is part of the autopsy. This examination should be conducted not only with the naked eye but with the dissecting microscope. The presence of one or two grains of powder on clothing does not necessarily mean that the deceased was shot at close range. Powder grains can travel as far as 20 ft from muzzle to clothing. Just as the powder gases produce alterations in the wounds on the body, so will they alter the appearance of bullet holes in the clothing. In contact wounds through clothing, depending on the type of fabric and the amount of gas produced, tearing and/or melting of the material can occur. This is true whether the garment is hanging loose or pulled tightly against the skin. Contact wounds in 100% synthetic material (nylon, triacetate, etc.) result not in tears but in “burn holes.” The heat of the gases causes the material to melt producing large circular holes, usually with scalloped margins. With large- and medium-caliber weapons, tears in material may occur not only at contact range but at near-contact range. Clothing can be ignited by close-range firing. This refers to black powder cartridges, however. Black powder emerging from the barrel is often still burning. It can land on clothing, continue to burn, and ignite the clothing. This does not occur with smokeless powder. Occasionally, a pillow is used to muffle a gunshot. If the weapon is a revolver, in addition to a blackened seared entrance hole, one can see a linear, an “L” or a “V” shaped blackened zone of seared material on the pillow where it was wrapped around the cylinder of the gun.  Measurement of the distance between this mark and the entrance hole will give one an idea of the barrel length of the weapon. If 100% synthetic material overlaps the cylinder gap, the gases may burn completely through the material. “Bullet wipe” is a gray to black rim around an entrance hole in clothing. It is seen around holes made by both lead and full metal-jacketed bullets. It is not, as some people contend, lead wiped off the bullet but is principally soot. Lubricant and small amounts of metallic elements from the primer, cartridge case, and bullet may also be present in the bullet wipe. The bullet carries all this material on itself to the target. As it passes through the clothing, it “wipes off” this material, producing the bullet wipe. If one thoroughly cleans the interior of a barrel until there is no material left in it and then fires a bullet down the barrel, this bullet on striking cloth will produce a light gray sometimes almost imperceptible bullet wipe. As more and more rounds of ammunition are discharged down the barrel, the bullet wipes produced will become increasingly darker in color until finally the color will stabilize as a dark black. Bullet wipe is seen in microscopic sections of entrance wounds as small particulate deposits of amorphous black material along the wound path. It is often mistakenly interpreted as “powder” and erroneously construed as evidence of a close range wound. Careful examination of both sides of a bullet hole in clothing, using a dissecting microscope, may suggest the direction in which the bullet was moving by which way the fibers are bent. Deposition of fragments of tissue on the inner surface of clothing around a bullet hole strongly suggests that it is an exit. In the case of wounds due to centerfire rifles, and rarely with handguns, tissue may also be blown out the entrance, and deposited on the inner surface of the cloth around the entrance. This is a result of positive pressure waves generated in the temporary cavity formed by the bullet. Although in many cases soot and powder grains are readily seen on the clothing, thus indicating a close-range shot, on occasion examination with the naked eye and the dissection microscope is insufficient. The powder may have fallen and/or bounced off, or one is at the extreme range at which powder exiting a barrel will have sufficient velocity to embed itself in the material. In such situations and in instances where an exact determination of the range may be necessary, rather than just saying it is close-range, an analytical examination of the clothing is desirable. The Modified Greiss test is the evolutionary end product of the Walker test. This latter test was developed to detect nitrite compounds produced by the burning of smokeless powder (cellulose nitrate). The Walker test documents the presence of nitrites as well as showing the size, configuration and density of the pattern on clothing or other objects. A firearms examiner can then attempt to duplicate this pattern by firing the same weapon and type of ammunition, at know distances, at the same type of material. The test involves desensitizing glossy, photographic paper in a hypobath, washing and drying it, immersing it in a 5% solution of sulfanilic acid; drying it, dipping the paper in a 0.5% solution of alpha-naphthylamine in methyl alcohol, drying the paper, placing the clothing to be examined on the paper, placing a layer of cloth moistened with 20% acetic acid over the clothing to be examined, and pressing down on this cloth with a warm iron for 5 to 10 min. The paper is removed and washed in hot water and methyl alcohol. When nitrites are present, they will appear as orange-red spots on the paper which when retained constitutes a permanent record of the presence and distribution of the nitrite compounds. A less commonly used method of examining clothing in order to make range determination involves the use of energy dispersive x-ray. The edges of the entrance hole are analyzed for the presence of antimony, barium, lead, and copper. Multiple readings are taken at varying distances from this hole. When rimfire ammunition containing only lead in the primer was fired at cloth, it was observed that one may detect antimony, barium, and lead. The source of the antimony and barium were deposits of antimony and barium in the bore of the weapon caused by previous firing of other rimfire ammunition that had these metals in their primers.

Determination as to whether a gunshot wound in a decomposing body is either close-range or distant can be difficult for a number of reasons. First are the changes of decomposition itself. Decomposition results in a blackish discoloration of the skin and subcutaneous tissue, which can either simulate or conceal soot. Blood around the wound clots and dries out. Fragments of this desiccated blood can simulate partly burnt powder fragments. Maggots and beetles are attracted to injury sites where blood is present. They can completely obliterate the entrance in the skin and thus any evidence of soot or powder. Insects can burrow into the skin, producing circular defects resembling gunshot entrance wounds. If there is subsequent drying of the edges, this may simulate the blackening and searing of a contact wound from a small caliber weapon. As mentioned, fragmented, dried-out, desiccated blood can simulate partly burnt grains of powder. The suspected material can be submitted for analysis by thin-layer chromatography. This latter method can differentiate single-from double-base powder as well. Determination that a defect in a body is a pseudo-gunshot wound caused by an insect, is usually made by examining the wound and attempting to follow its bullet track. Usually, the insect burrows down only to the subcutaneous tissue and it is obvious that one is dealing with an insect defect.

Acknowledgements:

The Police Department;

www.politie.nl and a Chief Inspector – Mr. Erik Akerboom     ©

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