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1.
Class Characteristics
We begin by reviewing several definitions of class characteristics compiled
from the literature. The authors’ choices of very different language to describe
similar observations about the class characteristics of shoes serves as a rea-
sonable starting point for this discussion. Osterburg (1968) describes them
as obvious, gross features distinguishable in an object. Cassidy (1980) was
more specific in describing them as the size, shape, style, and pattern of an
object, all created during their manufacture, and Bodziak (1990) explains
* Although electronic evidence such as audio or video recordings are not generally processed
by most crime laboratories, they frequently comprise important evidence in a case and are
sent out to be examined by specialists. Because electronic playback devices are necessary
to even hear or see them, they strictly involve more than just our sense of hearing.
Testimonial evidence, such as a confession, would require just human senses, but is not
something most analysts would encounter. Another example involving sound is the deter-
mination of whether a gunshot could have been heard at some distance under particular
conditions. This might involve the use of a decibel meter.
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Principles and Practice of Criminalistics
that they are intentional or unavoidable characteristics that repeat during the
manufacturing process and are shared by one or more other shoes.
Extending that thinking to other objects, items exhibiting similar char-
acteristics, as detected by the tests performed, comprise a class defined by
those characteristics. We can perform a visual test on all of the pencils in a
large office. Yellow pencils form a large class, yellow #2 pencils may form a
subset of that class, and yellow #2 pencils with erasers make up an even
smaller category. All pencils that are some color other than yellow, a different
grade from #2, or lack erasers are excluded from the third and smallest class.
We arrive at a definition of class characteristics:
The traits that determine class characteristics are intrinsic to the material itself;
without these traits, the object or material would be something else. For
example, a pencil with graphite tightly embedded into the middle of a piece
of cedar is known as a wooden pencil; a pencil with reloadable graphite sticks
is known as a mechanical pencil. While both might be classified on one level
as pencils, we have no difficulty further refining the classification into wooden
pencils and mechanical pencils. We would not confuse the two (although we
might not be able to differentiate writing made with one or the other).
One consequence of classifying something as belonging to a particular
group containing similar items is that we exclude it from other groups. At
its most trivial, this means that by classifying something as a hair, we exclude
it from the class of trucks. In other words, classification is just as important
for what it excludes as for what it includes. More pragmatically, if an analyst
can say that the hair belongs to the category containing cat hair, it is, by
definition, excluded from the class containing human hair. Classification can
answer important questions and allows some intelligent decisions to be made
on the basis of the determination. The classification as a cat hair may also
raise other questions that were not issues before the analysis; for instance,
can the hair be traced to the victim’s cat? The foregoing also suggests an
analytical approach to the classification of materials; if you cannot prove
what it is, prove what it is not.