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Firearms Examiner Training

Biological Evidence

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Biological Evidence

Biological evidence consists of body fluids or other bodily tissues, the examination of which may identify the donor.


  • Blood
  • Semen
  • Saliva
  • Bone
  • Hair
  • Skin


Mobile evidence-drying cabinet
Mobile evidence-drying cabinet
Image courtesy of Tri-Tech Inc., Southport, NC (see reuse policy).

The power of DNA testing is such that examination of biological items can produce very compelling evidence. However, attention must be paid to degradation, contamination, and safety issues.

Although DNA is chemically robust, it can be degraded by environmental factors such as moisture and sunlight. It is recommended that biological evidence be air dried as soon as possible and is always kept in paper packaging. The techniques used to develop DNA profiles are extremely sensitive. It is important to wear protective clothing (e.g., gloves and face masks) during collection and handling to prevent contamination from other biological factors, such as sweat and saliva.



Protective clothing
Protective clothing
National Institute of Justice (NIJ) (see reuse policy).

Blood can contain pathogens such as the Hepatitis B virus, Hepatitis C virus, and the human immunodeficiency virus (HIV). It is essential to regard all biological evidence as potentially infectious and to follow universal safety precautions.

These precautions include the following:

  • Wear personal protective equipment (PPE), such as gloves and face masks.
  • Avoid eating, applying cosmetics, or any hand-to-face contact (especially mouth and eye).
  • Use implements and wear puncture resistant gloves to handle objects that may have been used for intravenous administration of drugs place these in sharps disposal containers.
  • Identify biohazardous evidence material and package in containers with appropriate labeling.

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