Examination of Firearms Review: 2007 to 2010 - Interpol

3.2 Estimation of shooting distance and bullet hole characterization
3.2.1 General considerations
The greatest part of GSR produced by a shooting is projected on the target
(object or victim) if this target is close enough to the shooter. The diameter and
the density of the GSR particle deposition pattern will help to determine the firing
distance. Moreover, the rotating bullet will usually produce a wipe ring around the
entrance hole. The presence or not of a wipe ring will help to state on the nature
of the bullet hole (entrance or exit).
When the nature of a wound is questionable (entrance or exit wound), some
research groups recommend to look at the presence of textile fibres (coming
from the victim’s clothing) since in case of an exit wound, textile fibres should be
absent. However Vennemann et al. (129) demonstrated that the presence of
textile fibres is not a suitable criterion to determine the nature of a wound since
the presence of textile fibres both from the entrance and exit holes could be
stated; moreover the density of the fibres along the bullet path seems to be
dependent of the length of this path and of the size of the temporary cavity.
3.2.2 Colour tests
Colour tests are usually needed to determine the firing distance and the nature of
bullet holes since the GSR pattern can be invisible due to lack of contrast
(especially for dark fabrics). Distance determination using colour tests are
essentially based on visual examination with the use of test firings at known
distance for comparison. The use of the same weapon and the same ammunition
is crucial since it will strongly affect the GSR pattern. This has already been
pointed out in many references. Another illustration of the influence of weapon
and ammunition is brought in reference (103).
The colour test of choice for the estimation of shooting distance and bullet hole
characterization is still the sodium rhodizonate test, specially sensitive to lead.
For instance a positive test with sodium rhodizonate is indicative of an entrance
hole. Bailey et al. (130) evaluated the limit of detectability, determined to be
approximately 160 ng Pb/cm². The test was positive for 35 different .22 calibre
ammunition with a shooting distance of 7.6 m, indicating a strong robustness of
the sodium rhodizonate test. In another study, Bailey et al. (131) tested 70 holes
due to air gun pellets, presumably less sensitive to the sodium rhodizonate test
since the wipe rings do not contain cartridge components such as primer
residues. About 60% of the pellet holes yielded a positive reaction for lead.
Haag (132) performed a study on ricochet marks. SEM/EDX was used in
conjunction with sodium rhodizonate and dithiooxamide (a colour test used for
the detection of copper). The use of SEM/EDX enhanced the initial information
obtained from the colour test by giving additional information that can help in
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