Examination of Firearms Review: 2007 to 2010 - Interpol

unused, deck shoes of poor manufacturing quality presenting manufacturing
defects resembling in shape wear accidental defects. This example supplements
previously published articles calling for caution in this respect. Although such
cases may be rare, inexperienced examiners should be aware of the potential for
manufacturing defects, especially when examining inexpensive footwear. Here,
again, knowledge of the manufacturing processes involved is essential.
Knowledge regarding the thread design of footwear outsoles is also crucial for
shoeprint identification. Adair (38) also reports a case where shoeprints in blood
were found in an assault scene. The impressions were comprised primarily of a
“double-helix” style pattern travelling lateral-medialy across the outsole. Some
“arms” of the double-helix pattern were incomplete, which suggested that one arm
might be slightly higher than the other. Initial search of outsole databases was
negative. The outsole pattern was eventually identified as a Nike Jordan B’2rue
brand shoe. The shoe pattern is remarkable in that one arm of the double-helix
design is slightly elevated above the other. This design is relevant to footwear
examiners since the impressions created by new shoes will appear quite different
than impressions created by heavily worn shoes. In a new, relatively unworn state,
the impressions created by this shoe will have only one arm of the double-helix
present in 2D impression. As the shoe wears, the pattern will begin to resemble
the double helix pattern.
2.3 Tire Tracks
Bodziak (39) published a comprehensive, well-written, sourcebook on the recovery
and the forensic examination of tire track evidence. This book covers all aspects of
tire impression examinations, from the design and manufacturing of tires, through
the examinations at the scene and the documentation of the tire tracks there, to
the examination at the lab and presentation in court. The book also includes
information regarding tire tread databases, like the Tread Design Guide (by Tire
Guides Inc., USA) and others.
The recording of known test impressions from a suspect vehicle was discussed by
several authors. Nause and Soulier (40) presented a simple and effective
technique, based on the use of spray-on cooking oil, black fingerprint powder, and
safety film, for the recording of tire impressions. This approach was found to be
user-friendly, used easily obtainable materials, and gave excellent results.
LeMay and colleagues (41) studied the effect of tire pressure and cargo weight on
the width of tire track impressions. These authors made test impressions of tires
with various air pressures and different weights of cargo in the vehicle in order to
determine whether the width of a tire impression changes based on those
variables. The results obtained suggest, not surprisingly, that the width of the
contact patch varies according to tire pressure and weight of cargo.
2.4 Test Impressions
Preparing the right test impression, from the suspect’s footwear, is sometimes the
basis for successful identification. Examiners occasionally find it necessary to
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