Author: William M. Davis
Abstract:
Because studies have shown varying amounts of gunshot
residue (GSR) in the police environment, with most being on surfaces within
facilities occupied and operated by law enforcement, the current study examined
whether GSR contamination could be found on the hands of detainees at the
Harris County Jail (Texas) who were not charged with any offenses related to
the discharge of a weapon.
Of the 175 samples obtained and tested, not one
characteristic GSR particle was found. Coupling the results of this study with
one in which no GSR particles were on 100 persons answering bench warrants in
Bexar County (Texas) gives an average of less than one GSR particle in 275 hand
samples. Considering that a different study of random surfaces within the
Chicago Police Department (n=201) found a total of 56 GSR particles, the
current study concludes that GSR particles are not readily transferred to surfaces
not in close proximity to a recently fired gun.
Applying the Poisson (counting) probability model to the
current combination of findings led to the probabilities that arise for the
detection of small numbers of GSR particles among populations inhabiting
facilities operated by law enforcement officers. The study recommends that a
best-practice for GSR analysis could be a threshold of three characteristic
Pb/Ba/Sb particles, since the presence of this number of particles is unlikely
to be found as the result of chance exposure. A higher threshold lessens the
probability further.
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