8127/frame/fm

 
Figure 4.6
 
Tool and mark.
A toolmark is a three-dimensional impression. How-
ever, so many variables are involved in producing the mark, that only one
dimension is normally used to conclude a common source between a tool and a
mark left by it.
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Principles and Practice of Criminalistics
three-dimensional information might be retained, or a track, where some
other medium (such as dust) is transferred to the target, and the dimension
of depth is lost. As we have previously mentioned, some material is trans-
ferred along with the print or track, but this is usually not the item of interest.
Rather, the shape of this transferred material provides more information
about the source than the material itself. In the case of shoe traits transferred
to a floor through the medium of dust, the medium communicates nothing
about the shoe itself.
The transfer of traits does not seem to fit into Locard’s writings, but we
believe that this is an appropriate expansion of his philosophy. One way to
think of transfer of either material or traits is at a level that unites them both,
the concept that what is being transferred is 
 
information
about the source of
the evidence. Understanding the nature of the evidence allows the analyst to
decide which information might be most useful in answering the relevant
question(s). It may be that analysis of both the shoe print and the dust in
which it is made will be useful in deciding where a particular shoe has trod.
It may also occur that an incomplete fingerprint can be analyzed for its DNA
content via the physiological fluids in which the print is made. When we
think of transfer in terms of the information gleaned about the source of
some evidence item, a new avenue of research is opened for forensic science
that relies on 
 
information theory