What is Associative Evidence in Forensic Science?
Associative evidence is any item of physical evidence that can establish a link or connection between two separate entities, such as a person, a place, or an object. Unlike evidence that identifies a substance (e.g., “this powder is cocaine”), the value of associative evidence lies in its ability to connect the critical components of an investigation: the suspect, the victim, and the crime scene.
The Purpose of Associative Evidence
The primary goal of identifying associative evidence is to establish a linkage and help reconstruct the events of a crime. It provides context and shows relationships between different elements. The key associations include:
- Linking a suspect to a crime scene: For example, a suspect’s fingerprints found on a weapon left at the scene.
- Linking a suspect to a victim: For example, the victim’s blood or DNA found on the suspect’s clothing.
- Linking a victim to a crime scene: For example, fibers from the victim’s sweater found in the room where the crime occurred.
Connection to Locard’s Principle
Associative evidence is the tangible result of Locard’s Exchange Principle. Locard’s principle states that “every contact leaves a trace,” and it is this “trace” that serves as the associative evidence. The fiber that is transferred from a suspect to a victim is the physical manifestation of the link between them.
Examples of Associative Evidence
Almost any form of physical evidence can be associative, depending on the context. Common examples include:
- Firearms Evidence: A cartridge case found at the scene that matches a suspect’s firearm.
- Trace Evidence: Hairs, textile fibers, soil, paint chips, or glass fragments.
- Biological Evidence: DNA, blood, semen, saliva, or skin cells.
- Pattern Evidence: Fingerprints, footprints, tire tracks, or tool marks.
