PHYSICAL EVIDENCE MANUAL - Crime Scene Investigator Network

Physical Evidence Manual
Safety and Contamination Prevention
Current DNA technology allows for very small amounts of sample to be analyzed.
For example, a blood stain the size of a sharpened pencil point may be enough
to perform DNA analysis on, as would the residue amount of sweat and skin cells
on the inside rim of a ball cap. Because of this, inadvertent contamination of the
evidence is possible if you do not take precautions.
• Wear gloves and, if desired, a mask and eye protection while collecting
biological samples.
• Change gloves frequently or anytime your gloves are contaminated with
biological material.
• Do not touch the tips of cotton swabs with your fingers.
• Avoid contaminating your swabs by getting them dirty, talking over them,
blowing on them to make samples dry faster, etc. Consider purchasing
individually wrapped sterile swabs.
• Do not touch your water dropper bottle tip to any surface or evidence.
• Clean tools (such as scissors or tweezers) that you might use to collect
evidence with a 10% bleach solution and dry thoroughly.
General Collection Guidelines
In general, wet or moist biological evidence should be dried if possible and
packaged into paper containers. Paper packaging prevents the evidence from
degrading, so wrapping the evidence first in plastic then placing that inside paper
(or vice versa) defeats the purpose. Mark the packaging with a “BIOHAZARD”
label.
Rules of thumb for long-term storage of biological evidence is refrigerate wet or
liquid evidence and freeze dry evidence.
UV Light Searches
Many officers chose to use an ultraviolet (UV) light, Woods lamp, or other
alternate light source to assist in the search for biological stains. Such devices
can be helpful in a search, given that many biological stains such as semen and
saliva may fluoresce, or appear bright, when viewed with UV light in a darkened
room.
However, there are three important points to remember when using a UV light to
assist your search for biological stains:
Adopted: May 2002
Revisions: 6
Last Revision: January 31, 2008
6-2