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Trace Evidence and the Prosecution. Mitch Poe, J.D. Tarrant County ADA Kelly L Belcher, M.S. Trace Analyst Patricia C. Eddings, B.S. Senior Trace Analyst. What is this?. Edmond Locard. 1877-1966

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Trace evidence and the prosecution

Trace Evidence and the Prosecution

Mitch Poe, J.D. Tarrant County ADA

Kelly L Belcher, M.S. Trace Analyst

Patricia C. Eddings, B.S. Senior Trace Analyst

Trace evidence and the prosecution

Edmond Locard


Enthusiastic French scientist who believed that a cross-transfer of materials occurred whenever two objects came into contact with each other.

Trace evidence and the prosecution

Locard’s Exchange Principle

Exchange Principle - 1928

Whenever two objects come into contact there is always a transfer of material. The methods of detection may not be sensitive enough to detect this or the decay rate may be so rapid that all evidence of transfer has vanished after a given time. Nonetheless, the transfer has taken place.

Trace evidence and the prosecution



Gunpowder and Gunshot Primer Residues

Ignitable Liquid Residues



Stains and “Stuff”

What is Trace Evidence?

What can trace evidence do for your case
What can Trace Evidence do for your case?

  • Provide Investigative Information

    • What type of car was used in a hit and run?

    • What is hair color from suspect’s hat at burglary scene?

  • May help with reconstruction

    • Associate people with objects, people with people, or objects with objects

    • Corroborate/refute witness statements

Trace analysis dna profiling
Trace Analysis ≠DNA Profiling

Know your case
Know Your Case

  • Know all the facts of your case

  • Know what all the physical evidence is and where it came from (Chain)

Know what you want
Know What You Want

  • What questions are you trying to answer?

  • Don’t just drop of case without instructions to laboratory

  • Depending on analysis – known standards

  • Communicate with laboratory personnel!

  • If there’s a DNA match, trace may not be necessary!!

Know the capabilities and limitations of your crime laboratories
Know the Capabilities and Limitations of Your Crime Laboratories

  • Sequence of Testing

  • How long does my test take?

  • Where is my case in the line?

  • How does cost affect my case?

Communicate with other persons involved in the case1
Communicate with Other Persons Involved in the Case Laboratories

  • Let partners know when your case is disposed

  • Keep partners informed of changes in direction of case

  • Trace is not the same as DNA.

  • Freely share information with partners

Ultimately communication to a jury
Ultimately: Communication to a Jury Laboratories

  • Unprepared = PAIN!!!

  • All work leads to this point

  • You must be a salesperson and your work is the product

  • Credibility means everything!