Biological Screening

  • Description
  • Frequently Asked Questions

The Biological Screening Section of the Crime Lab analyzes evidence found at a crime scene or associated with a criminal investigation and attempts to isolate any biological material which can be linked to a victim or a suspect. Analysts in the Biological Screening Section deal with such offenses as homicide and sexual assault and perform the following functions on a regular basis:

  • Screen evidence for biological material
  • Document the evidence, both in writing and with digital imaging
  • Collect and preserve all potential evidence found
  • Attempt to identify biological material through chemical and immunological tests
  • Testify in court as an expert witness

Blood, saliva, semen, vaginal samples, and stains are examined and analyzed. Items such as drink containers, envelopes and stamps, human bodies, steering wheels, and knife handles are swabbed to isolate DNA from lick marks, bite marks, or handprints. Fingernail scrapings or swabs of body parts are preserved for DNA analysis.

This Section answers such questions as “Is this red stain human blood, or is it fish blood or even lipstick?” Once biological evidence is isolated, DNA analysis can be performed to establish the identity of the donor. This identification and characterization can implicate or eliminate a suspect and assists investigators as they reconstruct the events of a crime.

Who collects evidence from a victim after an alleged sexual assault?

A Sexual Assault Response Team (SART) nurse or a doctor will normally perform an examination, collect samples of potential biological evidence, and document the findings. Often a victim advocate will be present to offer support and information to the victim.

Who collects physical evidence from a suspect after an alleged sexual assault?

Law enforcement officers are trained to collect biological evidence from suspects and will normally perform this as part of their investigation of an assault incident.

How long does biological evidence of a sexual assault remain on a suspect's body?

The Crime Laboratory will not usually examine suspect specimens that are collected more than 48 hours after an offense, and biological material does not normally remain after 24 hours due to showering and hand washing.

Can the Crime Laboratory determine if a blood stain is from a moose, fish, or a person?

The Crime Laboratory can differentiate between human and non-human sources. Human blood can be further identified by DNA as to the actual identity of the person in cases where that person's DNA makeup is known. For differentiation of various animal species, a laboratory such as the National Fish and Wildlife Forensics Laboratory in Ashland, Oregon is utilized.