Physical Evidence in Criminal Investigations

Direct evidence

Direct evidence proves a fact conclusively.

Circumstantial evidence

Circumstantial evidence involves facts that require inference to prove the fact at issue.

Physical evidence

Reconstruction of the crime scene, determining if a crime occurred, linking individuals to crime scenes or other individuals, and providing investigative leads.

Locard Exchange Principle

It explains that whenever two individuals come into contact, there is a transfer of materials between them.

Linkage evidence

Evidence that shows a contact between individuals or between an individual and a crime scene, such as hairs, fibers, or bloodstains.

Advantages of physical evidence

Physical evidence is tangible, not subject to memory loss, and cannot be distorted by the defendant.

Preservation of physical evidence

Improper handling can compromise the evidence, leading to wrongful convictions or the failure to convict guilty parties.

Class characteristics

Types of physical evidence that are considered to have only class characteristics include glass, soil, and fibers.

Exemplar

A sample prepared from a known source for comparison with a questioned item.

Comparison standards

Materials collected from a known source for comparison with questioned evidence to determine if they share the same origin.

Chain of custody

The documented process of evidence handling, ensuring its integrity and preventing tampering.

Scientific requirement for evidence collection

Evidence must be protected from contamination by limiting scene access, preventing casual inspection, and using proper packaging.