What principle is often summarized by the phrase "every contact leaves a trace" in crime scene processing?

The principle summarized by the phrase "every contact leaves a trace" is known as the Locard Exchange Principle. This forensic concept implies that whenever two objects come into contact with one another, there is always a transfer of material from one to the other. In the context of crime scene investigation, it means that a perpetrator will bring something into the crime scene and leave with something from it, which can include hair, fibers, fingerprints, or other types of evidence.

This principle is foundational in forensic science as it underscores the importance of meticulously documenting and analyzing all potential evidence at a crime scene. It serves to establish connections between suspects, victims, and locations, making it vital for investigators to consider how evidence can link individuals to a crime through the traces they leave behind.

In contrast, the other principles mentioned focus on different aspects of the legal and forensic process, such as the preservation of evidence (chain of custody), legal guidelines for evidence admissibility (exclusionary rule), or specific federal regulations regarding evidence presentation (Federal Evidence Rule). None of these encapsulate the critical concept of material transfer that the Locard Exchange Principle highlights.