Trace Trace Evidence Evidence and the and the

ProsecutionProsecutionMitch Poe, J.D.Mitch Poe, J.D. Tarrant County ADA Tarrant County ADAKelly L Belcher, M.S. Trace AnalystKelly L Belcher, M.S. Trace AnalystPatricia C. Eddings, B.S. Senior Trace AnalystPatricia C. Eddings, B.S. Senior Trace Analyst

What is this?What is this?

Edmond LocardEdmond Locard1877-1966

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

Locard’s Exchange Locard’s Exchange PrinciplePrinciple

Exchange Principle - 1928Whenever 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.

What is Trace What is Trace Evidence?Evidence?

• Hairs• Fibers• Gunpowder

and Gunshot Primer Residues

• Ignitable Liquid Residues

• Glass • Paint• Stains and

“Stuff”

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

Hit and RunHit and Run

Trace Analysis Trace Analysis ≠≠

DNA ProfilingDNA Profiling

Prosecution PerspectiveProsecution Perspective

Know Your CaseKnow 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 WantKnow 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 Know the Capabilities and Limitations of Your and Limitations of Your

Crime LaboratoriesCrime 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 Communicate with Other Persons Other Persons

Involved in the CaseInvolved in the Case

Communicate with Communicate with Other Persons Other Persons

Involved in the CaseInvolved in the Case• 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 Ultimately: Communication to a Juryto a Jury

• Unprepared = PAIN!!!• All work leads to this point• You must be a salesperson and

your work is the product• Credibility means everything!