Fire Scene Evidence Collection Guide

Bodily Fluids

Saliva

Detailed Procedure:

Saliva is typically found on a substrate, most often a cigarette, sealed envelope, stamp, or eating/drinking utensil.

To collect an item with a questioned saliva stain:

  1. Saliva is a bodily fluid. When collecting, observe Universal Precautions. Wear new, unused, clean latex or nitrile gloves. Wear respiratory and eye protection as needed.

  2. Photograph the saliva-stained item in place.

  3. If the entire item bearing the saliva stain can be collected, collect the entire item. If the saliva stain is wet, place the item on new, clean, dry paper. Place the item and paper in a draft-free, dry location that is secure, ensuring no one will touch, step on, remove, or displace the item. Allow the item to air dry. Do not package the item when wet; it may putrefy and therefore lose its evidentiary value.

  4. When the item is dry, insert it into an appropriately sized, air-permeable but closed container, such as a cardboard box, paper envelope, or paper bag. Do not fold the item unless it is absolutely necessary. If the item must be folded, protect the stained area with a piece of paper and avoid folding across the stained area.

  5. If the saliva is on an immovable surface, like a tile floor, it can be collected using an absorbent medium, such as a new, clean, sterile cotton gauze pad.

    1. Open the gauze pad packaging and lay the pad on the saliva stain. Allow the pad time to absorb the saliva. If the pool is not sufficient for absorption into a sterile cotton gauze pad, collect the stain using a sterile swab, rubbing it over the stain to remove as much of the saliva as possible. Be sure to concentrate as much saliva as possible on each swab (ie: two swabs with concentrated amounts of saliva are better than six swabs slightly stained with saliva).

    2. Air dry the gauze pad or swab before packaging by laying it on a clean sheet of paper or hanging it up, at room temperature, away from direct heat, sunlight, and drafts. If saliva evidence items are not dried before packaging, they may putrefy and therefore be unusable.

    3. Before inserting the gauze pad or swab into the envelope, label the container with identifying information, including case number, date, exhibit number, a brief description, and your name. Once the gauze pad or swab is dry, place it into a clean, new evidence collection envelope. If swabs are being collected, insert them cotton tip first into the envelope.

    4. Submit a new, unused gauze pad or swab in a separate container as a control sample.

  6. Seal the container(s) with tape, not your own saliva. Initial and date the tape.

  7. Store the item in a secure, temperature-controlled location, such as a refrigerator or climate-controlled evidence storage room, until you are able to transport it to the laboratory. Do not leave the swabs or biological evidence in a hot car.

If you are unsure how to collect saliva or a saliva-stained item, document the item photographically and contact your forensic laboratory for guidance before proceeding with collection procedures. If the saliva-stained item will also be examined for ignitable liquid residue, please consult the laboratory for the proper collection procedure. Items should not be air-dried or packaged in an air-permeable container if they will be examined for ignitable liquid residue.

Laboratory testing of saliva:

If skin cells are present, the saliva samples can be examined to determine nuclear DNA profile (sex is determined during the DNA analysis). Blood type may also be determined by saliva. Comparison of a questioned nuclear DNA profile to a known profile is possible. Comparison of nuclear DNA profile to other profiles via computerized database (eg: CODIS for DNA profiles) may be possible.

Known DNA samples:

Generally, known DNA is collected using a buccal swab. Please contact your forensic laboratory for assistance. A court order may be required to collect this type of sample.

 

Source:

Crime Scene and Evidence Collection Handbook. Bureau of Alcohol, Tobacco, Firearms and Explosives, 2005.

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