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Trace

The trace section uses a wide variety of microscopes, instruments and chemical testing techniques to examine several different types of evidence. The examination of fire debris evidence and chemical unknowns are included in the tests performed in the trace section at the MN BCA Forensic Science Service. 

Fire Debris Introduction

Chemical Unknown Analysis

Many of the examinations the trace section performs involve the comparison of two or more objects to see if they could have had a common source.  We analyze the chemical, physical, and optical characteristics of the evidence and draw conclusions.  The Locard Exchange Principal is one of the principal theories that this type of trace evidence is based on.  A French scientist, Edmund Locard (1877-1966) theorized that each time two objects come in contact with one another there is an exchange of material.  Trace evidence helps solve crimes by linking people, places, and things involved in a crime by the microscopic materials they transfer through contact.

Here are some examples:

  • A hair found on a hat left at a scene compared to a known hair sample from a suspect.
  • Glass found on a suspect’s clothes compared to glass from the scene.
  • Shoeprints left at a scene compared to shoes from the suspect. 
  • Tape from a bound victim compared to a roll of tape from the suspect’s car.