From: gmk@terpsichore.MAE.CWRU.Edu (Geoff Kotzar)
Subject: Re: Gunshot Residue Forensics (LONG Reply)
Date: 11 Aug 1994 17:56:16 -0400
In article <firstname.lastname@example.org>, email@example.com
(David W. Taylor) writes:
|> In article <firstname.lastname@example.org> <email@example.com> writes:
|> #I recall reading that one of the problems with the Vince Foster lab results
|> #was that his clothes were left unpackaged several days in the lab in a
|> #ventilated room, and therefor the powder residues found could well have
|> #been contamination brought in by the room fan. It seems that if people are
|> #in frequent contact with residues, by cleaning guns, etc. such lab tests
|> #would not point to anything specific.
|> I also understand , from a source that I believe to at least be knowlegable
|> that some food preservatives and treatments can simulate the powder
|> residues. IE: German sausage, Salami, Hotdogs(Nitrate compounds).
|> At least this can trigger the portable test the officers use in the
|> spray can. I would assume (Hopefully) that a hard analysis in a lab
|> would not make this mistake.
I have read a number of replies to this posting. I appologize for taking so long
to bring the text in from home and replying, but much of what was said by the
respondents was not correct and needs clarification.
The following is from "Gunshot Injuries" by Vincent J.M. DiMaio from the
Elsevier Series in Practical Aspects of Criminal and Forensic Investigations.
The following is summarized from Chapter 12: Detection of Gunshot Residues pp
"At present, there are three generally accepted methods of analyzing for gunshot
residues: neutron activation analysis, FAAS, and analysis using the scanning
electron microscope. All three tests are based on the detection of barium,
antimony and lead originating in primers and deposited on the back on the hand
firing the weapon."
FAAS stands for flameless atomic absorption (spectrum).
The residue is acquired for testing by swabbing the hands with cotton swabs
dipped in 5% nitric or hydrochloric acid. The regions swabbed are generally
from the web between the first and second fingers back to the wrist and over
to the thumb. The four surfaces are the ventral and dorsal surfaces, palm and
back respectively, of the trigger finger and thumb of both hands.
For certain cases of suicide the whole palm or back of the non-gun hand may be
swabbed. This is a function of how the gun was held. Also if the individual was
a shooting victim the disposition of the residue would be, commonly, on the
palms exclusively (from holding the hands out to ward off the threat) unless
the hand(s) were completely engulfed by the muzzleblast. In this case there
might be residue on the backs as well.
"In the author's laboratory, levels of antimony, barium and lead are considered
significant only when they are at or above 35ng for antimony, 150 ng for barium
and 800ng for lead. For a hand washing to be positive for a CENTERFIRE weapon,
all three elements must be present and at least the lead must be elevated.
Marked elevation of barium alone may be due to the presence of soil rich in
barium on the hand."
I emphasized the word CENTERFIRE above because only centerfire primers currently
contain all three metals in their primers. Rimfire primers are a differennt
matter. For example, Remington rimfire priming compound only has lead, CCI and
Winchester have lead and barium, while Federal has all three. GECO, he claims,
has an indoor 9mm load which has no lead or barium. Also is has a fully enclosed
lead core so no lead is vaporized from the base of the bullet upon firing.
DiMaio lists 9 cases as examples of how the metals are deposited and explains
which are significant.
He has a number of VERY interesting things to say on the subject as well.
First, the difficulty with FAAS and neutron activation "is that one can never
be assured absolutely that one is dealing with firearms' residues. Both
methods of analysis are bulk, elemental analytical methods involving
measurement of the total quantity of metallic residues involved. One cannot
distinguish the source of the metals. In addition, both techniques have a high
percentage of FALSE negatives. If one asks 100 individuals to fire 100
different centerfire handguns, in only 40% to 50% of the individuals will the
hasndgun washings be positive. This percentage is even lower for rimfire
weapons. In living individuals, as the time interval between firing an taking
the samples increases, there is a rapid loss of residue from the hands. This is
produced not only by washing the hands but just by rubbing them against
SEM techniques look for micrometer-sized particles of a characteristic shape the
elemental content of which are analyzed by x-ray analysis. The particles are
lifted off with adhesive. "Based on testing, it has been found that in indivi-
duals who have fired handguns, 90% of the time residue will be detectable, for
rifles and shotguns the figure is 50%." "Analysis on the hands of firers by SEM
has been positive for as long as 12 hours after they fired the weapon."
"Some police agencies in an attempt to link a gun to an individual use a trace
metal detection technique(TMDT). These tests depend on the detection of trace
metals left on the hand as a result of handling a gun." The metals form charac-
teristic color complexes with reagents that are sprayed on the hand. Different
metals produce different colors and can actually produce an image of the metal
object held. Whether the pattern and color are present depend on how long the
metal and whether the individual was sweating. As sweating increases, the color
and pattern increase in prominence.
The original TMDT used a 0.2% 8-hydroxyquinoline solution for viewing under UV
lighting. Positive results could be obtained for as long as 36 to 48 hours
after handling METAL. This is actually a weakness with this method. Since most
of the images are not sharp but rather difuse, the pattern could be from a
firearm or from a jack when you rotated your tires one or two days before or
from running your hand down an iron railing. A newer reagent,
2-nitroso-1-naphthol, does not require UV for viewing and is only sensitive for
about 4 hours after handling the metal.
The problem inherent with both TMDT's are their lack of specificity. DiMaio
conclused "Thus, in actual practice this test is more subjective than
You should note that nowhere in this chapter does DiMaio discuss "nitrates"; all
of the detection techniques require metal deposits. Nitrite testing is commonly
performed on clothing to determine the RANGE from muzzle to victim, however.
I hope this clears up some of the mis-information that has been previously
There are 11 references provided by the author as well for those wishing to know