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iii.
Trace.
One of the most important historical figures in forensic science,
Edmund Locard, popularized perhaps the most nebulous category of physical
evidence, trace evidence. Locard was a pupil of Alexander Lacassagne in
forensic medicine at the University of Lyons, France, and eventually suc-
ceeded him to that position. In Lyons, Locard also established the first police
laboratory in 1910. The concept of transfer, with which history credits
Locard, and with which Locard credits Alexandre Lacassagne, Arthur Conan
Doyle, and Hans Gross, was a turning point in the conceptualization of
forensic science; we discuss it at length later in this chapter. Locard wrote
profusely and produced many volumes dedicated to the tortured description
of various 
 
dusts
, 
 
mud
, and 
 
grime
that might indicate a person’s whereabouts
or occupation. However, the very nature of trace evidence — that it is every-
where — also undermines its potential significance; it is notoriously difficult
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36
Principles and Practice of Criminalistics
to determine the strength of trace evidence. Although several investigators
have attempted to estimate the frequency of particular fiber or particle in the
environment,* only rarely are the results from a particular case considered
in a quantitative manner (Houck, 1999). A major advance in trace analysis
was something as simple as the invention of the tape lift by Swiss criminalist,
Max Frei-Sulzer (Thorwald, 1966). A tape lift preserves the spatial orientation
of the particles and fibers to the item as well as to each other, adding a useful
second dimension to the interpretation. Because, by definition, the analysis
of trace depends on optical magnification, its development coincides with
refinements in microscopy. Without question, the polarizing microscope,
invented in 1828 by William Nichol (Solbello, 1999), has been the most
influential tool in the study of trace evidence.