The advent of new technologies such as DNA typing, the weight
of scientific evidence in criminal trials of widespread publicity, and
the proliferation of fictional and non-fictional works in popular media
have contributed to making forensic science well known, although
perhaps not as well understood, by the general public. One
of the consequences of this popularisation of forensic science was a
sharp change in the attitude of investigators, who increasingly tend
to delegate to scientists the collection of information necessary to
identify the perpetrator of the crime. However, the prominent focus
on the search of biological traces or fingerprints, due to their high
potential for the personal identification of the individuals present at
the crime scene, somewhat fade the interest towards other kinds of
evidence, such as trace evidence. This kind of evidence is in fact
perceived by judges and lawyers as less informative, because they
think that “all plastic items are the same”, i.e. that it is impossible to
discriminate among mass produced items. The purpose of this paper
is to stress that, with sound methods for interpreting evidence, it
is possible to improve the communication between the scientist and
the Court, and to show the real significance of the analytical results,
in the context of the case.
The analysis of the traces found on a knife used in a murder
case were performed by optical microscopy, IR spectroscopy, and
UV-visible spectroscopy. The interpretation of evidence was carried
out according to a Bayesian approach.
A description of the interpretation of evidence in a case in
which fibres were the key evidence. It is shown that the key aspects
for having a high value of the evidence are the circumstances of the
case and the reconstruction of the events given by the prosecutor
and by the defence, in addition of course to a sound analytical procedure.
In other words, it is shown that in some cases the evidential
value of fibres or other trace evidence can be very high, sometimes
comparable to that of fingerprints or DNA: when properly interpreted,
trace evidence can give key information for solving cases.
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