Examination of Firearms Review: 2007 to 2010 - Interpol

make 3D test impressions of footwear when they are comparing the footwear to
photographs of 3D crime scene impressions or to castings of these impressions.
There are several products available for such use. Some are polymers that require
mixing and hardening, and others are foam products that do not render fine detail.
A new product, Bubber (Delta, Sweden), was recently tested by LeMay (42) and
was found to be very easy to use and superior to other commonly-used products.
It rendered very fine detail that could be photographed and cast with dental stone.
This product may be used for preparing 3D test impressions from tires as well.
2.5 The Evidential Value of Shoeprints Examination
As discussed earlier in this Review, the identification of shoeprints is derived from
individual characteristics found both in the suspects’ shoe outsole and in the crime
scene impressions. In other, more frequent, cases, where no individual features
can be identified, the examination conclusion is of the form “the examined
footwear could have left the questioned impression from the crime scene”. In such
cases, the evidential value of the results is often misunderstood and undervalued.
LeMay (43) has recently discussed this issue, stressing the argument that even
when only class characteristics (like outsole design, actual size and wear) are
found, it is highly inclusive in nature, and must be treated as valuable evidence.
Footwear impressions found at a scene are simply too far beyond coincidental to
be dismissed. The example presented in this article is of a Nike athletic shoe,
which was distributed in the USA in numbers exceeding 280,000 pairs (of this
specific outsole thread design). That is less than 0.2% of all shoe pairs distributed
annually in the USA at that time (44), while not yet taking into account the shoe
size and wear.
It should be mentioned at this point that popular footwear brands, like Nike, suffer
from counterfeits of their products, thus the distribution figures presented by these
firms do not necessarily represent the actual share of any given outsole design in
the footwear population. A paper by Wisbey (45), which focused on the Nike Air
Force One sneakers, highlights some of the methods that assist the shoeprint
examiners assessing likelihood that a submitted sneaker may be counterfeit.
Petraco and et al (46) applied statistical techniques used in facial pattern
recognition, to a minimal set of information collected from accidental patterns in
five pairs of similar footwear (all of the same make, model and size), in order to
assess the evidential value of individual characteristics. In order to maximize the
amount of potential similarity between patterns, these authors only used the
coordinate locations of accidental marks to characterize the entire pattern. It was
found that in 20–30 dimensional principal component (PC) space (99.5% variance
retained), patterns from the same shoe, even at different points in time, tended to
cluster closer to each other than patterns from different shoes. This study is
intended to be a starting point for future research into building statistical models on
the formation and evolution of accidental patterns.
The Bayesian approach, advocated in the last decades by many forensic scientists
for the application in various disciplines, has not yet been fully studied for footwear
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