Examination of Firearms Review: 2007 to 2010 - Interpol

proper probability based fracture match reasoning and reporting, but also that
automated methods should not be used or applied blindly.
In a yet-unpublished report, following Tsach et al (119), Yekutieli et al (120)
demonstrated a prototype system used for physical matching in 2D. The system
has two main functions: One is to assist forensic experts in performing physical
matching in an objective manner, and the second - collecting statistics and build
confidence levels regarding physical matches. The probability distribution
functions (PDFs) of matching error values, for correct matches and for nonmatches
were estimated. This analysis was applied for different fracture line
lengths and three different materials. Eventually, these authors were able to
calculate error rates much more reliably than previous estimates. With the results
of this research, an expert can express his findings in a more numerical way, and
the Daubert criteria for a potential or known error rate can be fulfilled. Surprisingly,
statistical results were much lower than initially expected, probably because these
authors used only the 2D fracture lines and not any additional information
commonly used in fracture match comparison, such as the 3D nature of some
fractures or any existing texture and graphic patterns on the surface or outer
border of the pieces to be compared.
As experience shows, the nature of the broken or the torn object can influence the
results of the match. When examining the torn edges of plastic tapes, differences
between the tape ends are sometimes observed, due to plastic deformation.
Weimar (121) studied this phenomenon, and developed a method of overcoming it
by heat treating the torn ends. According to this author, heat treatment of the
examined PVC tapes made it easier to find corresponding tear edges, and the
conclusiveness of the found match was increased. Because the vast amount of
available different tapes, it is recommended to test the influence of heat treatment
on tapes encountered in each case, while taking into consideration other types of
evidences that might be influence by such treatment (fingerprints, DNA etc.).
This type of evidence is extremely useful in the investigation of road accidents,
especially in Hit-and-Run ones. Christophe and Daniels (122) presented a case of
matching a wood chip found at the scene with a wooden pallet that had been on
the back of the suspect's pick-up truck. The authors used Adobe Photoshop CS2
software for superimposing the images of the two exhibits. Based on their
examination of the surface contours of both items, a positive identification of the
suspect’s vehicle with the accident scene was established.
Other application of physical match may be in question document examination.
Guscott (123) study a case of analysing several threat letters, one of which aimed
at the local police department. Forensic document examination of the initial threat
letter established a link between the multiple cases in the neighbourhood. This
particular case involved multiple aspects of forensic document examination,
including handwriting identification, indented writing, the discovery of an ink defect
in the printing process of a notepad and a crease in another notebook, and a
physical match that proved the connection between the different cases. The
results of the forensic document examinations proved vital in securing a
conviction.
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