DNA testing and analysis

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 Interpreting genetic materials to assist in investigating the identity of a perpetrator or victim, particularly in criminal investigations.

Sources of DNA Evidence

The biological material used to determine a DNA profile include blood, semen, saliva, urine, feces, hair, teeth, bone, tissue and cells.

Samples that May be Used

Investigators collect items that could have been touched or worn by persons involved in a crime. The following items may contain DNA material:

  1. Masks
  2. Hats
  3. Gloves
  4. Clothing
  5. Tools
  6. Weapons
  7. Sexual assault evidence kits
  8. Underclothes
  9. Bedding
  10. Dirty laundry
  11. Fingernail scrapings
  12. Cups/bottles
  13. Cigarettes
  14. Toothpicks
  15. Toothbrush
  16. Facial tissue
  17. Hairbrush
  18. Eyeglasses
  19. Condoms
  20. Tape
  21. Ligatures (rope, wire, cords)
  22. Stamps or envelopes



The best evidence occurs when a person’s DNA is found where it is not supposed to be. For example, consider a breaking-and-entering that occurred in a residential area. Near the point of forced entry, a knit cap was found which the homeowners confirm was not theirs. Several head hairs were recovered from the inside, one of which had a root with tissue attached, which made it possible to obtain a DNA profile. The DNA profile was used to identify the perpetrator.

As technology advances, forensic scientists are able to analyze smaller and smaller biological samples to develop a DNA profile. For example, if a person touched an object or weapon, skin cells may have been left behind. This low-level DNA is sometimes referred to as “touch DNA”. It can even be collected from a victim’s skin or bruises where they were handled roughly. Low-level DNA samples may be helpful when examining evidence where it would be difficult to retrieve fingerprints—such as textured surfaces on gun handles or automobile dashboards. However, not all jurisdictions have the capability to process this evidence.

To compare the victim’s or suspect’s DNA profile to the recovered crime-scene DNA, the laboratory will need to have their known biological samples available for a side-by-side comparison. These known samples are called reference samples. In some jurisdictions, a DNA sample is routinely taken from an arrestee during the process of booking and fingerprinting. However, this is an evolving area of law and states vary in their laws governing the collection of DNA from arrestees. Sometimes a court order is required to retrieve a reference from a person of interest. Reference samples are always collected from victims unless they choose not to cooperate with the investigation; in that case, a court order might be required.   

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