Introduction To Trace Evidence

Locard Exchange Principle

A foundational concept in forensic science that states whenever a person comes into contact with an object or another person, a transfer of material occurs, which can be used as evidence. Explains why evidence moves

What types of trace evidence are there?

Hair, fibers, DNA, glass, paint, soil, cosmetics, dust.

What legal context does trace evidence need?

Types

Amount (more → more significant)

Location: helps collaborate on a story

Circumstance of the crime.

Class Evidence vs Individual Evidence

Class: group evidence → not specific source (usually most trace)

Ex: men buying a pack of 5 white t-shirts. Glass same composition

Individual: sends us back to the specific source: glass → fitting into broken window. Back to that location.

What do negative findings of trace evidence mean?

It doesn’t mean contact didn’t occur, just means nothing was left.

Good vs Bad Complexity of Trace Evidence

Good: conviction → more complex variation (tons of fibers), narrows down possibilities if found since the evidence is so complex.

Bad: time-consuming the because of variety, which takes more time for comparisons to be done.

Taping:

putting a piece of tape on object and lifting.

complex → picking up everything

Rapid process.

Tweezers:

Less complex → picking up one hair on item

Rapid

Could miss evidence

Vacuuming

Rapid

Complex → picking up everything

Difference between 1980 & today?

1980: was before good DNA analysis, detection methods weren’t really scientific valid, so studies and calculations were done. Relied more on eye witness, circumstantial evidence, and associative.

Today: expectation of DNA, more reliable and relevant.

CSI effect

Jurors expect DNA, more critical of other fornesic science, more confident on own verdict. dont look at the evidence provided, instead ask why certain evidence isn’t shown.

NAS report

• 2006 congress pased act science, state, Justice, Commerce, and related agency’s.

• Focused on analysis techniques using the scientific method, changed the standards on testimony wording.

• Revealed issues: faulty techniques

• Helped improve reliability, wrongful conviction and enchanced national security

NCFS

National Center for Forensic Science?

Conducts basic and applied scientific research in forensic disciplines such as biological evidence (e.g., DNA), physical evidence (e.g., fire debris, explosives), and digital evidence

SWGMAT

SWGMAT stands for Scientific Working Group on Materials Analysis & Trace. It’s part of a network of SWGs (Scientific Working Groups) in forensic science that create guidelines and standards for forensic disciplines.

• Develops best practices and standard protocols for collecting, analyzing, and interpreting trace evidence in forensic investigations.

• Helps labs maintain consistency, reliability, and scientific validity across cases.