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3.
Limitations of Reconstruction
Before attempting a reconstruction, the criminalist is well advised to recall
one of our favorite aphorisms:
Unless we have articulated competing hypotheses, it is much too easy to see
the evidence and information that supports one hypothesis without subject-
ing it to rigorous criticism. It becomes easy to dismiss evidence that does not
fit and emphasize evidence that does. This leads to two common problems
in reconstruction, overinterpretation of the evidence and attempting to re-
create the incident.
We see what we expect to see.
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Principles and Practice of Criminalistics
The farther we travel from source determination, the greater the number
of assumptions we incorporate into our inferences. At the level of reconstruc-
tion, all of the previous assumptions are implicitly incorporated, and more
assumptions are added. Sometimes, the assumptions may outweigh the facts;
change any in the complex web of assumptions, and the conclusion may
change. Many reconstructions simply reflect one person’s view of how the
events transpired. Because neither the facts nor the assumptions on which
reconstructions stand are often challenged, it is both easy and tempting to
allow our personal biases and expectations to drive our conclusions.
a.
Bias and Expectation
The temptation to overinterpret evidence or create reenactments results from
a generally unconscious expectation on the part of the analyst, that a partic-
ular cause is responsible for a specific effect. Common phrases revealing this
bias are typically encountered when reconstructing suicides. Such phrases as
“no one would do that,” “it’s too hard that way,” or (our favorite) “no one in
their right mind would do that,” are frequently heard. These reveal a subtle
bias; how would I perform this act, or how would I react to it? How one
person might contemplate suicide is of no consequence to how anyone else
might try to accomplish it. In particular, people committing suicide may or
may not be in their right mind, so this may not be taken as a limitation on
how the incident was accomplished. Frequently, this bias is revealed in reports
with expressions that include “it is reasonable,” “it is probable,” or “it is likely,”
with absolutely no reference to any facts or information to support them.
An analyst’s experience is a second source of expectation; when I see that
an action results in a particular consequence once, I expect that the next time
I see the effect, it will have resulted from the same cause. This is less serious
if the analyst uses the expectation as one hypothesis, but it is bias if it becomes
the only hypothesis. Experience should widen the analyst’s expectation, not
narrow it.
The end result of expectation based on personal bias and experience is
the introduction into the reconstruction of nuance and emotion that is not
supported by the physical evidence. A criminalistics examination may not
always, or not even frequently, culminate in a reconstruction. But when it
does, the role of the forensic scientist is to provide scientifically defensible
information about the sequence of events. Other speculative elements reveal
bias based on personal expectations, and reduce the credibility of the scientist
and the reconstruction itself.