Brazoria County Sheriff's Office
Identification Division
Crime Scene Investigation |
When dealing with sexual assaults, the investigator usually
has a living victim who can provide the investigator with information which will help in
collecting and preserving the pertinent evidence. The investigator should glean as much
information as possible, so he or she will know which evidence to collect. For example, if
the victim tells the investigator (which in this case may be the examining physician) that
no oral penetration occurred, then the investigator knows that no oral swabs will need to
be taken. Any information should be passed on to the crime lab, so the forensic scientists
will know how to process the evidence submitted. Evidence should never be submitted
without communicating relevant information.
When dealing with sex crimes, the victim should be taken to the hospital immediately and
the examination started as soon as possible. Photographs should be taken to document any
injuries which the victim received. If necessary, oral, vaginal, and/or anal swabs should
be taken from the victim and air dried for one hour in a moving air source as soon as
possible. They should be collected as soon as possible because the body begins breaking
down the various components in seminal fluid through drainage, enzyme activity, pH, etc.
The swabs should be air dried under a fan for at least one hour. This can either be
accomplished by the doctor at the hospital, or, upon collecting the kit from the doctor,
the investigator should bring it immediately to a secure place and air dry it. The reason
for this is that the moisture in the swabs allows microorganisms to grow which can destroy
the evidentiary value of the swabs. Known saliva samples from the victim must also be air
dried along with any other wet or moist samples (not including whole blood samples,
vaginal washing or any other liquid samples collected).
Usually, the best sample of seminal fluid comes from the swabs, as long as they are
preserved properly. The next best place is usually the victim's panties because the
seminal fluid will drain into the panties (if the assault was vaginal or anal in nature).
The stain will sometimes be better preserved because the seminal fluid tends to dry faster
in the panties. If the panties have wet stains, then they should be air dried as soon as
possible before packaging. Clothes can be a good source of seminal fluid if the assailant
ejaculated on the victim's clothes. The clothes can also be a source for the suspect's
blood, hairs, fibers, or other evidence transferred to the victim from the suspect.
Clothing should be air dried before permanent packaging and each article of clothing
should be packaged separately.
Bed sheets, comforters, spreads, etc. can also be a source of evidence from the suspect.
The value of this type of evidence should be carefully considered by the investigator
before collecting it. If the bed is a "high traffic" area, meaning that numerous
people have had access to the bed and the bed sheets haven't been cleaned in a long time,
then it won't have as much evidentiary value as a bed where only one person had access to
it and the sheets have been cleaned recently. The investigator should use the side
lighting technique to look for any loose trace evidence on the sheets which may be lost
during handling and packaging. This evidence should be placed in a paper packet and then
placed in an envelope. If the sheets have wet stains and these can be attributed to the
rape, then the investigator should circle these stains and inform the crime lab that those
are the relevant stains to be examined. The investigator should note that he or she
circled the stains and as always, air dry the evidence before permanently packaging it.
The investigator should neatly fold the sheets inward to prevent the loss of any other
loose evidence. The sheets can then be packaged separately in paper bags, air dried if
necessary, and submitted to the crime lab.
If a suspect is established in a rape case, then reference samples should be collected
from the suspect for comparison. These samples should include: a whole blood sample in a
red, yellow, or purple top "Vacutainer"; a saliva sample (air dried); 15-20
pulled head hairs; and 15-20 pulled pubic hairs. If the suspect is captured within 24
hours and it can be established which clothes and/or shoes he wore during the attack, then
the items should be packaged separately and submitted to the crime lab. Sometimes trace
evidence from the victim such as hairs, fibers, blood, etc. can be found on the suspect's
clothing.
The key to proper collection, preservation, analysis, and overall usefulness of evidence
is open and plentiful communication between investigators, forensic scientists, and
prosecutors. This will make the most of the evidence which can make or break a case. This
paper has presented general guidelines on the collection and preservation of evidence. The
investigator should remember that each crime scene is different and each crime scene is a
learning process. The investigator should also keep in mind that different crime labs may
like their evidence collected in different manners. This is why the investigator should
not hesitate to call his or her crime lab if he or has a question or a problem on the
collection or preservation of evidence.