Examination of Firearms Review: 2007 to 2010 - Interpol

et al (75) discuss the advantages of using the SEM for examining deep-seated
marks, and review the various imaging capabilities of this instrument. In order to
show the usefulness of the proposed approach, SEM and conventional optical
microscopy were used to examine firing-pin impressions in 9mm cartridge cases,
and the power of the SEM was demonstrated.
Katterwe and his colleagues (76) also describe the use of a comparison-SEM for
forensic applications, and present the “next generation” of such instruments – the
comparison variable-pressure SEM (VP-SEM). The conventional comparison SEM
comprises of two SEMs linked together trough a mutual control system, so that the
two instruments are synchronized electronically into a single video screen. The
comparison VP-SEM overcomes one of the limitations of the conventional SEM,
which is the need for conducting samples, thus enabling the relatively simple (but
quite expensive, NL) examinations of non-conductive specimens (made of plastic,
wood etc.).
In his previously-mentioned report, Prokoski (17) also studied the application of an
infrared (IR) imaging system for examining and matching of toolmarks created by
screwdrivers. The resulting marks were imaged using an IR camera with 640x512
detector array and 3X optics and also a visible light 2592x1944 CCD camera. The
IR images produced more consistent striations than the visible light images. The
study goal was to demonstrate whether IR was superior to visible light imaging
with respect to accuracy of match for 20 toolmarks against the database of 200
marks. The method for matching striations was a comparison of “barcode”
representations of "cut-lines" through the toolmark perpendicular to the direction of
the mark. As a result, each of the 20 IR secondary marks was correctly matched to
the primary mark made by the same tool.
3.3 Marks Produces by Various Types of Tools
Since the evidential value of toolmark examinations rests on the “uniqueness” of
the mark producing surface, knowledge of the manufacturing processes of various
types of tools is an essential part in these examinations.
Lang and Klees (77), while discussing the broader issue of forensic drill bit
examinations, including use indicators, swarf (cuttings) composition, etc., deal also
with the toolmarks left by these items. Two types of marks may be encountered
when drilling: marks on the work piece (especially in partially-drilled holes), and
those found on the remaining swarf. The reproducibility of toolmarks on certain
types of swarf is presented, and the application of these examinations in
improvised explosive devices (IEDs) cases is demonstrated.
Marking stamps (punches) are used for producing imprints, usually on metal
surfaces. Comparing such marks with the suspect stamps may have important
value in cases like forgeries of vehicle chassis and engine numbers. Weimar and
his colleagues (78) describe in detail the manufacturing processes involved in the
production of these punched, and the implications of each method on the expected
toolmarks produced. These authors conclude that the punches produced by the
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