8127/frame/fm

 
5.
Physical Evidence: From Art to Science
Any endeavor, when performed at its pinnacle, is an art. The genius inherent
in a musical prodigy is not fundamentally different from the genius required
to solve a recalcitrant mathematical proof (Hofstadter, 1979). Both require
a leap beyond pedestrian rationality and the courage and faith to take that
leap. Scientific breakthroughs stand on a bedrock of many small, insignificant
advances; but the final solution is often rooted in an intuition that is not
fully understandable based simply on previous data.* We do not mean to
imply that a forensic analysis is an act of genius, only that the boundaries
between art and science are perhaps less distinct than is commonly under-
stood. The nature of forensic science lends itself to an artistic and intuitive
approach. Facts are often in short supply, analytical results are rarely text-
book, and human nature prompts us to fill in the gaps. The very recognition
of this proclivity, however, and the institution of rigorous review procedures,
serves as an effective counter to our natural tendencies.
At the same time that we strive to maintain scientific objectivity, however,
we must realize that the comparison between evidence and reference, regard-
less of whether the items of interest are two fingerprints or two spectra, is
not free of human subjectivity. Nor should it be. Two items derived from the
same source are nevertheless two unique items, having experienced different
paths through time and space. The question before the forensic scientist is
not, as the uninitiated might assume, are these two items the same, but rather,
can we exclude the possibility that they originate from the same source? Even
the most-sophisticated instrumentation cannot overcome imperfections in
the samples themselves; analysts must rely on their education, training, and
experience to determine whether small differences observed between evi-
dence and reference samples qualify as 
 
significant
or 
 
explainable
. It is worth
* In an interview with John Horgan for 
 
The End of Science
, Karl Popper insisted that a
scientific theory is an invention, an act of creation as profoundly mysterious as anything
in the arts (Horgan, 1996).
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Introduction
13
emphasizing that training in any of the forensic disciplines includes (or at
least should include) examining many patterns, some of which are known
to come from the same source and some of which come from different sources
(Murdock and Biasotti, 1997). It is the process of testing the limits — gaining
experience with the variation that occurs in samples from the same source
and knowledge of the similarity that samples from different sources might
exhibit — that generates an appropriately skeptical and cautious, yet confi-
dent, examiner.
Because this process of comparison, and the expertise to accomplish it,
is acquired through a lifetime of trial and error, it is not always a conscious
process. Part of the effort in systematizing a body of knowledge is to explicate
the guidelines for the interpretation of a particular type of analysis. This not
only encourages consistency by compelling the analyst to consciously define
the comparison process, but also allows other colleagues working in the field
to understand the guidelines by which an analyst has arrived at a conclusion.
The explication, organization, and dissemination of a common set of ground
rules provide a universal starting point for critical review by both peers and
independent reviewers. However, no matter how clear and well reasoned the
guidelines, and no matter how conscientiously applied, two competent sci-
entists may still ultimately disagree about the interpretation of a result. This
is simply the nature of science. One could program a computer with all the
interpretation guidelines in the world, but a human being still must designate
and input the guidelines. Two computers, programmed with different inter-
pretational guidelines, may also assert different conclusions.
One effort in this direction has been standardization. Is standardization
the answer? To some extent, yes. Standardization allows scientists to begin
the discussion on common ground, understand each other’s data, and share
results. However, to constrict an analyst to a particular detail in some ana-
lytical procedure, or to a set of immutable interpretational rules, risks mis-
analyzing or misinterpreting any particular piece of evidence, the special
nature of which might have been unforeseen at the time the guidelines were
established. And if anything is true about forensic evidence, it cannot be
predicted. Thinking is allowed.
It is crucial to recognize that, even among physical evidence, some cate-
gories may not fit a traditional or commonly understood definition of science,