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D.
Individualization
In “The Ontogeny of Criminalistics,” Kirk (1963) proffers individualization
as that unique aspect of criminalistics that establishes it as a discipline in its
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Classification, Identification, and Individualization
123
own right. While not all evidence is either potentially or necessarily individ-
ualizable, the concept remains the hallmark of our profession. To the extent
that naming a material satisfies the law, identification is invoked. When the
objective is to establish the source of an object, the process of individualiza-
tion must be used. We spend the remainder of this chapter exploring the
questions and assumptions, the pitfalls and quagmires, that we encounter in
the process of individualization.
 
1.
A Conclusion of Common Source
Criminalists today agree that the goal of individualization is an inference of
singular common source. That is, two objects are concluded to share a com-
mon origin if they were at one time contiguous (physical matching) or if
they both originate from the same unique source. Examples include evidence
and reference bullets fired from the same weapon, evidence and reference
prints from the same shoe, and pieces of paper that were once one. Implied
is the expectation that no other source could have produced both items. This
defines the key difference between individualization and classification. When
a substance or object is classified, multiple sources remain possible; when it
is individualized, the number of possible sources is narrowed to one. The
distinction between classification and individualization can be summarized
as 
 
one-to-many
vs. 
 
one-to-one
(see Figure 6.2). Note that these phrases
describe the 
 
relationship
between source and item, not any physical attribute
of an object or substance itself.