Investigators should perform the evidence collection process in a systematic and careful manner.
The process begins with the preliminary crime scene survey/walk-through, followed by a determination of the evidence collection sequence to be used.
The evidence collection sequence may be based on the following information:
• The scene location: interior, exterior, within a vehicle.
• The condition of the evidence: either fragile or stable.
• Weather conditions which might affect the scene or evidence within.
• Scene management considerations which may alter or contaminate the evidence.
• Additional processing techniques that may need to be conducted at the scene with specialized personnel.
Investigators should use the appropriate equipment when collecting evidence. Collection equipment that may come into contact with evidence should be sterile.
The following equipment may be used in the evidence collection process:
• Latex gloves/nitrile gloves (N-DEX, non-latex).
• Paper bags.
• Plastic bags.
• Cardboard boxes.
• Wrapping paper.
• Hand tools.
• Plastic 5 gallon bucket with lid.
The swabbing collection technique should be used for the recovery of biological evidence in a dried or liquid state. Best practice techniques include the following:
DRIED MATERIAL COLLECTION TECHNIQUE
• With gloved hands, slightly moisten the swab with distilled water. (The swab should be damp but not overly wet.)
• Thoroughly rub the stained area using a single moistened swab for a small stain and multiple swabs for a large stain. When only a small amount of the stain is available, concentrate as much of the stain as possible on the tip of the swab.
• Air-dry the swabs.
• Place each swab into separate package.
• This package may be placed inside a paper envelope.
• Collect a substrate/control sample from an unstained area using the same techniques.
LIQUID MATERIAL COLLECTION TECHNIQUE
A. When suspected biological evidence is found on clothing or other absorbent surfaces transport it to the laboratory in an appropriate container. Wet evidence should not be folded over on itself. Use paper wrapping to prevent contamination during the transfer. This will protect bloodstain patterns and prevent cross-contamination between stains on one item. The item should be air-dried thoroughly in a drying locker and packaged in a container suitable for dried evidence.
B. If the suspected biological evidence is in a liquid form on a fixed surface that cannot be transported (i.e., concrete floor), the substance should be recovered using the following swab technique:
1. With gloved hands, swab the liquid material allowing the swab to absorb as much of the substance as possible. Multiple swabs should be obtained when a large quantity is available.
2. Thoroughly air-dry each swab.
Package the swab inside an appropriate container.
3. Collect a substrate/control sample from an unstained area using the same techniques.