8127/frame/fm

 
2.
Spatial Trait Transfer
 
a.
Impression Evidence
Although we are used to thinking about transfer of physical material, many
criminalistic examinations deal with traits or characteristics of one item left
behind on some receptive medium, rather than any transfer of actual physical
material. Dermal ridge prints, shoeprints, and tire tracks all fall into this
category. This may be accomplished by 
 
impressing
the traits into the medium
(e.g., a toolmark), or leaving the trait as a 
 
print
or 
 
track
on a substrate via
yet another medium (e.g., a fingerprint left in naturals oils and perspiration
from the finger). One can think of these mechanisms as transfers as well;
however, in these cases traits rather than matter are transferred.
 
b.
Three- to Two- to One-Dimensional Transformations
In most types of trait transfer, some dimensional information is lost. For
example, in a toolmark, the mechanism for producing a mark is usually the
passing of a defect in the tool over some target material. This defect may be
a gouge or a protrusion, and has three dimensions (Figure 4.6). When exam-
ining the mark made on the substrate, normally only one of the dimensions
8127/frame/ch04 Page 96 Friday, July 21, 2000 11:48 AM

---

The Origin of Evidence — Divisible Matter and Transfer
97
(width) is used for comparison. The length is lost in the process of producing
the mark, and the depth is highly dependent on a number of factors, such
as the relative hardness of the two media (source and target) and the angle
between them. Thus, a three-dimensional defect is reduced to a one-dimen-
sional mark.
In friction ridge examinations, normally only one dimension coupled with
spatial information is used to compare evidence and reference prints. Some
examiners will perform a more complex analysis involving the integration of
pore placement and the shape of the ridges themselves. Nonetheless, the
fingerprint examiner is restricted to an analysis of at most two dimensions.
Shoeprints and tire prints hold the potential for including all three
dimensions, but typically this examination is done using only width and
length data (two dimensions). The number of dimensions available for exam-
ination ultimately depends on whether the mark is an impression, where