Examination of Firearms Review: 2007 to 2010 - Interpol

a different shape, but may also show a different composition from the particles
which were air-borne. Primers containing low-melting point metals like tin may
produce particles which solidify after hitting the substrate (the surface of the
cartridge case), although sometimes tin is present in the air-borne particles, but
absent in the case particles. This suggests that tin in these particles originates
not from the primer itself but from the bullet jacket. Thus, in the interpretation of
the GSR analysis results not only the primer composition needs to be taken into
account, but also the materials used in the manufacture of the bullet and jacket
and the gun itself play an important role. Evidently, linking the composition of
airborne GSR to the GSR in the cartridge case sometimes requires that
laboratory experiments be performed under controlled conditions. This can of
course only be done if the ballistic elements are present.
In a second study, she investigated whether the GSR particle composition varies
in different locations around the firearm/shooter (123). In this study, a Luger 9
mm ammunition was fired from a pistol and samples collected from the shooter
(hands, sleeves, front and back of the upper clothing) and the target at 50 cm. In
a separate experiment, particles were collected from cotton targets, placed at five
different distances up to one meter from the shooter. Trying to model the
dispersion behaviour of the particles both in the shooting direction and in the
opposite direction, links to the behaviour of the particles using the physical
properties of dimension and density of the several types of particles were made.
The author concludes that it is possible to observe differences in the composition
of particles found on the hands of the shooter and on his clothing: the first
originate from the ejection port of the gun, while the latter are partly coming from
back-draft turbulence as the gaseous stream that follows the bullet through the
barrel emerges from the muzzle and is distributed in all directions by the
turbulent expansion in the air. The particles on the clothing of the shooter would
therefore resemble more the particles found on a nearby target and contain more
material coming from the bullet base, while the case/ejection port/hand samples
would be constituted solely of material coming from the primer.
Finally, Rijnders et al. (124) performed a comparable study using four types of
ammunition (two classic, one titanium-zinc and one titanium-zinc doped with
gadolinium) of the same calibre (9 mm) and one pistol. Samples were acquired
from seven positions in and around the firearm, simulating both the shooter
(clothing and hands), the target, and the gun/case internals. The particles were
analysed by SEM/EDX and classified into 16 particle classes, specially designed
for these experiments. Next, a statistical approach was used to calculate
Pearson correlation coefficients. Using these statistics, a number of conclusions
can be drawn: it is possible to distinguish between different ammunition types
(from the set of chosen ammunition), internal samples from barrel and chamber
correlate badly with external samples (hands, target, case) – an explanation for
this may be found in the memory effect of the gun, while a good correlation can
be seen in the samples of the shooters’ hand and victim. Also, according to this
study, the results from the case samples correlated badly with the other samples,
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