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Collecting DNA Evidence at Property Crime Scenes

Dry Stains on Non-Absorbent Surfaces

Dry Stains on Non-Absorbent Surfaces

Collection procedures for dry stains on nonabsorbent surfaces are as follows:

  • Submit the entire item, if possible. (Note: If the entire item is submitted and it is a sharp object such as broken glass, it will need to be safely packaged in cardboard and labeled "sharp object enclosed.")
  • Use a new or clean scalpel blade to scrape the stains from the surface.
  • Collect the flakes onto clean paper and fold the paper in a bindle.
  • If the stain is on wood, shave the area of the bloodstain with a new or clean scalpel blade.
  • Package each item separately.
  • Place sample in a labeled envelope that provides reference information on where the sample was collected.
  • Take a control swabbing from unstained areas using a new sterile swab slightly moistened with distilled water. Allow the control swab to air-dry, label and package in paper.
  • If determined by your agency protocol, collect the sample with tape using the following procedure:
    1. Place fingerprint tape (do not touch sticky surface with bare hands) over bloodstain and surrounding negative control area.
    2. Rub nonsticky side of tape with a pencil eraser or other blunt object. This is to ensure that good contact is made between the stain and the tape.
    3. Lift the bloodstain like a fingerprint and place the tape on an acetate backing. (Do NOT use a paper backing — paper makes the stain difficult to handle during analysis). The lifting process can be repeated several times on the same stain if necessary.
    4. Label the stain(s) and package individually in a paper envelope.

Advantages: The dilution and contamination potential is minimized by eliminating the use of water as the collection medium; a control is readily collected; it requires little storage space and is a fairly easy technique to perform.

Disadvantages: Investigator must decide which stains to collect; bloodstains do not lift well off certain surfaces. A potential drawback to this method is possible touch DNA contamination if the investigator repeatedly reaches into a common tape lift bag or handles the sample using nonclean techniques.

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