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159
determine whether the accused has committed a crime, by hearing
evidence
for and against the proposition. While we have covered the topic of legal
evidence in Chapter 5, its definition is crucial to the discussion of association,
and so we briefly repeat it here.
Relevant evidence means evidence having any tendency to make the exist-
ence of any fact that is of consequence to the determination of the action
more probable or less probable than it would be without the evidence.
The law places physical evidence in the category of circumstantial evidence.*
One characteristic of circumstantial evidence is that it requires an inference to
connect the evidentiary fact with a principal fact in the case. For physical evi-
dence, this means connecting the results of an analysis for source determination,
by means of an inference, with the proposition
that the defendant committed
the crime. We have previously distinguished between identification evidence
(e.g., drug possession, blood alcohol concentration) and potentially individu-
alizing evidence. Because identification evidence is, in effect, direct evidence, it
does not require an inference of association to establish its relevance. Therefore,
any further reference to physical evidence in this chapter will be, by definition,
to potentially individualizing evidence for which we have established a common
source between an evidence sample and a reference sample.
Science, on the other hand, perceives physical
evidence primarily as
tangible evidence that we can detect with one of our five senses, and that is
amenable to some analytical technique. Because a court will not admit irrel-
evant evidence to be heard by the fact finder, however, the results of a
physical
evidence examination must lead to an inference that makes the existence of
a legal fact (Is the suspect guilty?) more or less probable than it would be
without the physical evidence. Without a showing of relevance, the physical
evidence may not be admitted. We assert that mere source determination
per se is not relevant to a legal proceeding. While Cook et al. (1998b) briefly
highlight this contention, it is not widely appreciated in scientific circles. If
you are not yet convinced, consider the following scenario:
• A fingerprint at the scene of a burglary is found and submitted to an
examiner. The examiner eliminates the current residents as a source
of the print, and determines from a search of the national fingerprint
database that it is from Fred Flintstone.
* Circumstantial evidence is that which is applied to the principal fact indirectly or through
the
medium of other facts, from which the principal fact is inferred. The characteristics
of circumstantial evidence, as distinguished from that which is direct, are (1) the existence
and presentation of one or more evidentiary facts and (2) a process of inference, by which
these facts are connected with the facts sought, tending to produce a persuasion of their
truth (Haight, 1996).
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Principles and
Practice of Criminalistics
This information is provided to the detective, who heaves a sigh of thanks
to the crime scene technician, the fingerprint examiner, and St. Paul of Kirk,
and sets out to locate the burglar. The detective stops short when she discovers
that:
• Fred Flintstone died 10 years before the crime was committed.
At first doubting the competency of the examination, she asks another fin-
gerprint analyst to compare the evidence and reference prints. The second
analyst confirms
the source determination, concluding that Fred Flintstone
left the print. The detective must now reconsider her theory of the case. Some
interesting possibilities occur to her, including:
1. The print was deposited at least 10 years ago, and is unrelated to the
current crime.
2. The print is a coincidental match.
3. The print was planted as a forgery.
As esoteric and unusual as these explanations might be, one of them must
be true, because it is impossible for Fred Flintstone to be implicated in the
current crime (unless, of course, Fred faked his death, and he is still out there
committing crimes). We note that fingerprint examiners
will resist alternative
2, while the detective might be willing to consider it. From this example, it
is clear that the mere existence of facts derived from an analysis of physical
evidence is insufficient to make it relevant. No one says it better than author
Conan Doyle, in the quote at the beginning of this chapter; a slight shift in
viewpoint and, all of a sudden, evidence that seemed immutably inculpatory
is suddenly irrelevant.
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