Examination of Firearms Review: 2007 to 2010 - Interpol

casework samples, and that the lack of statistical data (unlike DNA analysis)
undermines the evidential value of the examination. In addition, Schwartz claims
that there are no enough studies regarding the differentiation between subclass
and individual characteristics.
In other articles, addressed to defence attorneys, Schwartz (104, 105) suggests a
line of questioning for cross examination of firearm and toolmark experts in court.
These articles are useful reading material for any forensic scientist in the field of
toolmarks examination, in particular when preparing for a court testimony.
As mentioned earlier, differentiating between known matches (KM) and known
non-matches (KNM) is particularly important because of the legal challenges that
examiners may face in court. Neel and Wells (106) performed a study in order to
quantify the difference between KM and KNM, for better understanding of these
definitions. Various toolmark sources were used, including two- and threedimensional
toolmarks. More than 4,000 striated toolmark comparisons were
examined for their Total Matching Lines (TML), Percent Matching Lines (%ML),
and Consecutively Matching Striae (CMS). The results obtained show that 2D and
3D KM and KNM are statistically distinguishable from one another.
Bachrach et al (107) report the application of confocal microscopy and white-light
interferometry for the acquisition of 3D (topographical) data of a considerable
number of striated toolmarks created under controlled conditions on a variety of
media. Toolmarks were produced using screwdrivers and tongue-and-groove
pliers. The obtained toolmarks were then evaluated using algorithms, and the
distributions of the degree of similarity values obtained from the comparison of
known matching and nonmatching pairs of marks were analysed using established
statistical technique. Empirical error rates were calculated as a metric of tool mark
individuality, where a low empirical error rate is indicative of high specificity and
repeatability. While it is not possible to prove uniqueness statistically (98), the
results of this study provide support for the concept that toolmarks contain
measurable features that exhibit a high degree of individuality.
During the aforementioned study, Chumbley et al (88) compared the results
obtained by using computerized analysis with those of toolmarks and firearms
examiners. During the 2008 AFTE Training Seminar, volunteers were solicited into
participating in the examination of the same toolmarks earlier evaluated by the
algorithm. The AFTE volunteers were asked to compare those samples that were
found to be most difficult for the computerised algorithm, but still no false positive
results were reported by any of the AFTE volunteers. They did, however reported
some false negative results, mainly in a specific pair of samples, probably due to
the fact that the tools were not available for examination. These finding are in
agreement with other reported studies (85, for instance).
An interesting study regarding the calculation of the theoretical significance of
matched bullets, but having impact on toolmark analysis as well, was published by
Howitt and co-authors (108). These authors present the derivation of the formulae
for calculating the probability for the correspondence of the impression marks on a
subject bullet to a random distribution of a similar number of marks on a suspect
71