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1.
Principle, Process, or Objective
In the last chapter, we introduced the idea that classification, identification, and
individualization all depend on understanding the fundamental nature of mat-
ter or, for our purposes, the 
 
nature of the evidence
. In this chapter, we expand
on the generation of material characteristics and the qualities of those charac-
teristics that allow identification or source determination. The process of indi-
vidualization leads to a conclusion of common source resulting from analytical
similarities between two items, usually a reference sample and an evidence
sample. Writers such as Kirk
(1953; 1974) and Tuthill
(1994) treat individual-
ization as a principle, but it seems to us that individualization is a 
 
process
that
relies on the principles of chemistry and physics directed to a specific end.
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Principles and Practice of Criminalistics
 
2.
The Question of Source
Both classification and individualization attempt to answer the question of
source. Rarely explicated, however, is the distinction between a conclusion
of source for classification and a conclusion of source for individualization.
Classification allows for multiple source items; the evidence may derive from
source A, but it could also have come from source X, Y, or Z, all of which
are indistinguishable from source A by the tests employed. The implication
of multiple potential sources is perhaps underappreciated by both students
and practitioners of criminalistics and often is not adequately conveyed to
attorneys. It is not only that several or many items belong to the same class
as the evidence and reference, it is that we cannot distinguish from which of
these potential sources the evidence originated.
In addition, the 
 
level of source
must be defined by the question. This is
determined by the legal requirements necessary to satisfy an element of a
crime. To clarify what we mean, let’s take an example of carpet fibers.
It may be sufficient to determine that the evidence is a carpet fiber. It may
be sufficient to show that it is a polyester carpet fiber. It may be sufficient
to show that it is a polyester carpet fiber manufactured by DuPont
®
. It may
be sufficient to show that it is a green carpet fiber manufactured by DuPont
in 1977. It may be sufficient to show that it is from 10,000 yards of green
carpet fiber manufactured by DuPont in 1977. It may be sufficient to show
that it is a green carpet fiber manufactured by DuPont in 1977 and that it
was distributed to 15 vehicle carpet installers. It may be sufficient to show
that it is a green carpet fiber manufactured by DuPont in 1977 that was
distributed to 15 carpet manufacturers, and that one of them installed 10
square feet in a specific van in 1978. Or you may need to know that it is a
green carpet fiber manufactured by DuPont in 1977, that it was installed in
a specific van in 1978, and that it came from just behind the driver’s seat
of the van as opposed to the area by the rear door.
If the question revolves around showing that the fiber came from a carpet
rather than a garment, it is only necessary to show that it is a carpet fiber, a
relatively simple proposition. If, on the other hand, the case turns on whether
this bloodstained carpet fiber came from just behind the driver’s seat of the
van as opposed to the area by the rear door, the analyst must consider whether
such a determination is even possible. The circumstances and the legal needs
of the case determine the level of source required.