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Categories of Evidence
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Categories of Evidence

Categories of Evidence
Evidence can be labeled in one of three categories.  Very small evidence is referred to as trace.  Serology refers to blood and its components.  All evidence needs to be labeled with case number, date, time, initials of collector, and destination.  Each piece of evidence is logged and sealed.

Body Materials

  • may be wet, dry, or trace
  • need control samples (samples from known source)
  • blood, saliva, urine, feces, semen, vomit, tissue, hair
  • blood, saliva, and semen can be typed by the A-B-O system
  • wet blood is collected in test tubes with the goal of at least 10 ccs
  • dry blood is scraped into an envelop or hydrated with distilled water
  • DNA, proteins, and enzymes can be identified in all body fluids
  • 80% of the population secretes their blood type in their saliva
  • DNA can be pulled from envelope seals, stamps, and even head bands


  • bullets and weapons including explosives and their parts
  • fibers from fabric, clothing, sheets, blankets, tarps, polymers, tape, rope
  • cigarette and cigar butts
  • soil
  • glass
  • charred debris
  • documents
  • paints and varnishes
  • tools
  • needles

Everything is photographed before it is handled.  All objects are picked up while wearing gloves and using tweezers.  Each object is packaged separately in a box, metal can, or paper bag/envelope.  Nothing is ever packaged in plastic.  Plastic retains heat and moisture, both of which promote growth of bacteria and mold.  Bacteria and mold can contaminate or destroy evidence.  Guns must be emptied and tied in a manner that prevents accidental firing.  Known samples from surrounding areas are taken whenever possible.  With soil, that means 1 cup is collected from several locations.  Don't try to match tools to their marks while on site.  This may compromise the evidence.  Send an evidence submission form to each delivery site.  Hand deliver chemicals, live ammunition, explosives, and biohazardous materials.


  • fingerprints, palmer, plantar, and lip prints
  • tire tracks
  • tool marks and newly damaged areas
  • bite marks and open wounds

Fingerprints may be classified as one of three types of impressions:

          plastic: in a soft, pliable surface (mud)

          visible: easily seen (blood or ink)

          latent: not visible but still present, may be developed (use dust)

Tools and damaged areas need to have casts made after photos are taken.  Known standards are collected for comparisons.  Bite marks and open wounds are photographed and washed in distilled water.  Water is collected to check for saliva.