8127/frame/fm

C.
Summary
In this chapter, we have concluded our discussion of the principles of crim-
inalistics. The profession’s understanding of the processes of association and
reconstruction, and their implications, remains underdeveloped. We have
outlined a number of areas that require greater thought and refinement by
the forensic science community. Nevertheless, we can articulate a couple of
points with which most analysts would agree. First, association is an inference
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Association and Reconstruction — Inference of Contact
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of contact between two objects, and is the only way in which legally relevant
evidence can be generated by a scientist. Mere source determination is not
legally relevant per se. Second, the analyst requires a broad case context to
most thoughtfully formulate the competing hypotheses and articulate the
accompanying assumptions.
Although not all practitioners would agree that an inference of contact
is best expressed using likelihood ratios, a growing community is learning
the benefits of interpreting the results of forensic examinations in a Bayesian
framework. Almost a decade ago, Stoney (1991) wrote, “The likelihood ratio
is a generalization of the more generally used ‘match frequencies,’ providing
a logical and theoretical framework for supporting the inference of contact.
The likelihood ratio incorporates quantitative data from the factors deemed
relevant from the broad case context (including databases needed for evi-
dence evaluation, and the incorporation of properly constructed match and
correspondence frequencies).” It is our opinion that this is the direction in
which forensic science should continue.
Reconstruction is an attempt to order several events from an incident in
time and space based on physical evidence. Although reconstruction has been
practiced by criminalists for as long as physical evidence has been examined,
the discipline as a whole has never been systematized and no general or guiding
principles have been articulated. A reconstruction builds on the facts estab-
lished by source determination and association, and, by default, also incorpo-
rates all of the assumptions that were made in those previous determinations.
Although reconstruction can be a valuable tool for both the investigation and
solution of crime, it must be performed by someone with the requisite expertise
to understand the physical evidence and the limitations of the process.