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a.
Collection Procedures
Although this is not intended to be a crime scene manual, it’s worth briefly
reviewing the collection and preservation of evidence. As in medicine, the
first rule of evidence collection is to 
 
do no further harm
. In general, any item
of evidence should be transported to the laboratory in as intact a form as
possible. Any piece of physical evidence that is small enough is simply pack-
aged appropriately, clearly labeled, and removed to the laboratory environ-
ment where it can be processed under controlled conditions. This may be
more practical in some cases than others. For example, bloodstains on a
cement wall must be separated from the wall because the wall is unlikely to
come to the laboratory. Indirect methods, such as tape lifts, vacuum sweep-
ing, scraping, swabbing, casting, and photography may be used to collect
evidence that is difficult to pick up and move. The specifics of these methods
Goals of Evidence Collection
1. Maintain physical integrity
2. Limit degradation
3. Prevent contamination
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Principles and Practice of Criminalistics
are reviewed elsewhere (e.g., Svensson and Wendel, 1955; Fisher, 1993; Ogle,
1995; Geberth, 1996).
 
b.
Preservation
We take a moment to highlight the different considerations in the preserva-
tion of biological and nonbiological evidence.
 
i.
Nonbiological evidence.
For larger items such as weapons, tools, and
vehicles, the greatest danger is in introducing prints, fibers, or particles not
originally present. The worst possible consequence of such adventitious con-
tamination is the possibility of a false association between the evidence and
a putative, inculpatory, source. Wearing gloves is becoming appropriately
more common at crime scenes even for the collection of nonbiological evi-
dence. It is crucial to recognize that for gloves to protect both the analyst
from the evidence and the evidence from the analyst effectively, they must
not only be worn but changed intelligently. For objects that may hold impres-
sions such as toolmarks, it is important to limit mechanical contact so the
impressions don’t become altered. Please do not try to fit the screwdriver the
burglar left at the scene into the pry mark in the door. Trace evidence on
either object would be compromised and the impression could be altered.
The collection of possible arson evidence is a special case. Because ignitable
fluids are extremely volatile, even at ambient temperature, they must be
collected in airtight cans such as unused paint cans.