What is the basic principle of crime scene investigation according to Edmond Locard?

The principle that "Every contact leaves a trace," articulated by Edmond Locard, emphasizes that whenever two objects come into contact, they exchange materials. In the context of crime scene investigation, this means that a perpetrator will invariably leave behind some form of evidence at the scene of a crime, whether it be physical traces like hair, fingerprints, or trace chemicals. This foundational concept underpins the entire field of forensic science, asserting that careful examination of a crime scene will yield crucial information that can link the suspect to the crime or assist in reconstructing the events that transpired.

This principle has significant implications for investigators as it guides them in how to approach crime scenes. It necessitates meticulous evidence collection, documentation, and analysis to identify any trace evidence present. By acknowledging that every contact leaves a trace, investigators are encouraged to pursue all potential sources of forensic evidence, thus enhancing the likelihood of solving cases and securing justice.