How to Collect Blood Evidence From a Crime Scene
by Because of the potential value of blood evidence, it is important to know and understand proper collection procedures. Blood found as evidence on a crime scene must be collected properly. Procedures for collecting various blood stains are also considered.
Blood is Important Evidence
Blood is often encountered when investigating a crime scene. It is important to collect blood stains correctly. The type of stain and the surface must be considered when collecting blood as evidence from a crime scene. If at all possible, the item with the blood stain should be collected in its entirety.
Try to Keep it Intact
With clothing, sheets, small objects, carpet, sheetrock, or other material that can be easily cut or collected as a whole, this is the best method. This not only provides samples of the blood, but it allows the blood stain pattern to remain intact. Intact blood stain patterns are useful for blood spatter analysis, which can be very helpful to the investigation. (Saferstein, 2009) Unfortunately, this is not always possible.
Collecting Samples with Swabs
The criminalist must collect samples of the blood stain when it cannot be brought back entirely. If the blood is still wet, it may be absorbed using a dry cloth or swab. The sample must be allowed to air dry prior to packaging in a paper bag or envelope.
If the stain is already dry, it may be scraped off, depending on the surface. The dry blood flakes may be placed in a paper bindle and evidence envelope. When the surface does not allow blood to be easily scraped off, a swab or cloth moistened with distilled water is used to absorb a sample. (Bucholtz & Lewis, 2005) The sample must then be allowed to air dry prior to packaging, again in a breathable container such as a paper bag or envelope. This prevents the growth of bacteria or mold, which would breakdown the samples and damage their evidential value; plastic containers should never be used for blood evidence samples.
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Rare Circumstances
In more rare cases, blood may be discovered in blood or water. This is the only time that samples should be placed in an airtight container and frozen. (Saferstein, 2009) It is important that all personnel understand the importance of blood and know proper collection and preservation procedures.
Follow Proper Departmental Procedures
Following proper blood collection procedures ensures that the evidence remains valuable. Failure to follow procedures may break the chain of custody or allow for deterioration of blood samples and evidence. This must be avoided because blood is so valuable to an investigation; it can be used for DNA typing, ABO blood typing, toxicology testing, and more. Often, the outcome of the case relies on this important biological evidence.
References
Bucholtz, A., & Lewis, J. (2005). Biological Evidence: Criminal Investigations Series. LawTech Custom Publishing.
Saferstein, R. (2009). Forensic Science: From the Crime Scene to the Crime Lab. Upper Saddle River, NJ: Prentice Hall.
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