8127/frame/fm

 
a.
Presumptive Testing
Sometimes, even if a stain is visible, it’s not clear whether or not it is worth
collecting. Is it blood or shoe polish? Is it semen or hair gel?* An initial deter-
mination may be made at the scene for the sole purpose of determining whether
an item deserves further testing. Because the tests that are simple enough to
use in the field do not provide conclusive results, the identity of the item must
always be verified by more discriminating testing in the laboratory
 
.
 
3.
Collection and Preservation
About the worst 
 
faux pas
one can make at a crime scene is failing to collect
vital evidence or, almost as bad, failing to collect it in a timely fashion. This
was manifest in 
 
Simpson
when it was revealed that a bloodstain on the back
gate was missed the first time around and only recognized and collected weeks
later (
 
People v. Simpson
, February 15). Everyone then got to argue about
whether the DNA from the gate was planted, because it appeared to be in better
shape than that from samples that had been collected immediately but stored
in plastic bags in a hot van. As we mentioned in a previous section, this is an
example of depreciation of evidence that was not recognized during the initial
scene search and promptly collected. This led directly to an attempt to deter-
mine if EDTA (a preservative used in tubes used for collecting blood) was
present, which in turn led to questions about the reliability and validity of
testing for EDTA in blood and blood stains (
 
People v. Simpson
, June 20, July 24).
Almost as bad as missing a crucial item of evidence is failing to discern
what is relevant and what is gratuitous. Collecting “everything” may result
in losing track of critical evidence under a mountain of extraneous stuff. This
only creates problems in tracking, storage, and decision making when it
comes time for the crime laboratory to actually examine the evidence. There
are limits to all good things, and knowing what to leave as well as what to
collect is one of the finer points of crime scene processing.
A criminalist was called to a scene in which the victim had been shot in the
head in the back seat of a car. This resulted in the deposition of hundreds
* 
 
There’s Something About Mary
, movie directed by Bobby and Peter Farrelly, 1998.
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Good Field Practice — Processing a Crime Scene
209
of drops of fine blood spatter on the back of the front seat. The spatter
pattern was obviously the result of a single event; this was not the question.
However, the body had been dumped elsewhere. The blood was to be
collected to answer the question, “Was it the victim’s blood?” The criminalist
meticulously collected each and every drop of the fine spatter separately.
Not one of the stains by itself was large enough to provide reliable biological
testing results. This time-consuming and thoughtless exercise could have
been avoided if the criminalist had simply formulated the relevant question
before beginning to collect evidence.
Collection and short-term preservation of the sample or item are insep-
arable. The moment one lifts a print or collects a stain, the evidence is altered
from its original form. Ideally, preservation issues will be considered in
determining the collection method. Probably the greatest distinction in col-
lection and preservation methods is determined by whether the evidence is
biological or nonbiological. The next section is divided into collection and
preservation suggestions determined by the type of evidence. The subsequent
discussion of contamination issues follows the same pattern, additionally
exploring the consequences of cross-contamination between biological and
nonbiological evidence.
A number of techniques have been developed to collect otherwise
immovable evidence. The collective (pun optional) goal of these techniques
is to: