PHYSICAL EVIDENCE MANUAL - Crime Scene Investigator Network
PHYSICAL EVIDENCE MANUAL - Crime Scene Investigator Network 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
Physical Evidence Manual 1. A number of other materials may also fluoresce, such as urine, stains from food or drink, laundry detergent, and many other substances. 2. Not all semen or saliva stains will necessarily fluoresce with a UV light. 3. Blood will not fluoresce when viewed with a UV light; rather, it will appear dark. Blood Evidence Blood evidence is common in violent crimes. In addition to DNA, blood contains cells and proteins that allow the laboratory to perform the following examinations: • Testing can determine if blood is human or non-human in origin. • The specific animal family can be determined for non-human blood. Collecting Liquid or Moist Blood – Large Quantity 1. Saturate several (5 to 10) sterile cotton swabs with the blood. Allow swabs to air-dry. 2. Venous blood will coagulate so it is important to collect a good mix of clotted cells and serum. 3. The dried swabs can be placed in a paper container (e.g. paper envelope or bag). 4. Do not lick envelope seals, as this is a safety and contamination hazard. Collecting Liquid or Moist Blood – Small Quantity 1. Limit the number of swabs. One-by-one use swabs to collect the blood, concentrating the blood onto each swab. Use as many swabs as needed until the entire stain is completely collected. 2. Allow swabs to air-dry. 3. The dried swabs can be placed in a paper container (e.g. paper envelope or bag). 4. Properly label and seal the container. Do not lick envelope seals as this is a safety and contamination hazard. Collecting Dried Blood If the stained object is transportable, submit the item intact. Dried blood may flake off an object, so be careful to seal all openings of a package. If it is not transportable, collect the blood by one of the following methods. Adopted: May 2002 Revisions: 6 Last Revision: January 31, 2008 6-3
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Physical Evidence Manual<br />
1. A number of other materials may also fluoresce, such as urine, stains from<br />
food or drink, laundry detergent, and many other substances.<br />
2. Not all semen or saliva stains will necessarily fluoresce with a UV light.<br />
3. Blood will not fluoresce when viewed with a UV light; rather, it will appear<br />
dark.<br />
Blood Evidence<br />
Blood evidence is common in violent crimes. In addition to DNA, blood contains<br />
cells and proteins that allow the laboratory to perform the following examinations:<br />
• Testing can determine if blood is human or non-human in origin.<br />
• The specific animal family can be determined for non-human blood.<br />
Collecting Liquid or Moist Blood – Large Quantity<br />
1. Saturate several (5 to 10) sterile cotton swabs with the blood. Allow swabs<br />
to air-dry.<br />
2. Venous blood will coagulate so it is important to collect a good mix of<br />
clotted cells and serum.<br />
3. The dried swabs can be placed in a paper container (e.g. paper envelope<br />
or bag).<br />
4. Do not lick envelope seals, as this is a safety and contamination hazard.<br />
Collecting Liquid or Moist Blood – Small Quantity<br />
1. Limit the number of swabs. One-by-one use swabs to collect the blood,<br />
concentrating the blood onto each swab. Use as many swabs as needed<br />
until the entire stain is completely collected.<br />
2. Allow swabs to air-dry.<br />
3. The dried swabs can be placed in a paper container (e.g. paper envelope<br />
or bag).<br />
4. Properly label and seal the container. Do not lick envelope seals as this is<br />
a safety and contamination hazard.<br />
Collecting Dried Blood<br />
If the stained object is transportable, submit the item intact. Dried blood may<br />
flake off an object, so be careful to seal all openings of a package. If it is not<br />
transportable, collect the blood by one of the following methods.<br />
Adopted: May 2002<br />
Revisions: 6<br />
Last Revision: January 31, 2008<br />
6-3