Examination of Firearms Review: 2007 to 2010 - Interpol

Preparation of the appropriate toolmarks standards, using the suspect’s tool, is an
issue as well. Toolmark test exemplars are usually produced by applying a tool's
working surface to a piece of soft metal such as lead, since the lead will replicate
the microscopic grooves of the tool surface without altering them. An alternative
material for the preparation of such marks was presented by Petraco and coauthors
(71), who proposed using commercially-available jewelry modeling waxes
for this purpose. The replicas obtained are accurate, precise, highly detailed, and
1:1 negative copies of the exemplar tool’s working surface. They reveal in fine
detail the class characteristics, wear patterns, damage, and accidental markings
present on a tool’s surface.
Proficiency test samples are required to be identical, so each and every participant
is analyzing or testing a similar sample. In order to produce test samples for the
ENFSI Expert Working Group Firearms and Gunshot Residue (EWG FA-GSR), a
procedure for a “mass-production” casting method for complex 3D objects (like
bullets, cartridge cases etc.) was developed by Koch and Katterwe (72).
Preparation of the test samples includes two stages: making the moulds (“negative
casting”) of transparent silicone rubber (Elastosil by Wacker) followed by casting
the samples into these moulds (“positive casting”). A detailed graphic description
of the procedure is included in the article. Using this approach, it is possible to
undertake proficiency testing in the field of firearm and toolmarks simultaneously,
with identical samples for each participant.
3.2 Observation and Imaging Methods
The use of 3D imaging technologies for the potential application in forensic firearm
and toolmark identification was evaluated by Bolton-King and her co-authors (73).
A review of state-of-the-art profiling systems is provided, and particular attention is
paid to the application of 3D imaging and recording technology to firearm
identification. Each technology tested uses a different technique or scientific
principle to capture topographic data, such as focus-variation microscopy, confocal
microscopy, point laser profilometry and vertical scanning interferometry. In order
to establish the capabilities and limitations of each technology qualitatively,
standard reference samples were used and a set of specific operational criteria
was devised for successful application in this field. The reference standard
included the National Institute of Standards and Technology (NIST) 'Standard
Bullet' in order to ensure that the evaluation represented the practical examination
of ballistic samples. Based on this research, it was concluded that focus-variation
microscopy is potentially the most useful approach for forensic examinations, in
terms of functionality and 3D imaging performance.
Ahvenainen et al (74) employed scanning white-light interferometry (SWLI) for
comparing toolmarks produced by diagonal cutters on copper wires. There results
suggest that SWLI may be applied as a quantitative method for forensic toolmark
study through its high-resolution digital 3D profiles.
The high depth-of-field required sometimes for toolmark examination (especially
on rough and un-even surfaces), and the high magnification needed, led to several
attempts for using scanning electron microscopy (SEM) for that purpose. Randich
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