What theory states that every contact leaves a trace of evidence?

The correct answer is Locard's Theory of Transference, which posits that every contact between an individual and a location, or between two individuals, results in the exchange of physical evidence. This principle is foundational in forensic science and criminal investigations, emphasizing that perpetrators of crimes will leave behind traces of their presence at the crime scene, and will also take away traces from that location.

In practical terms, this means that forensic scientists can find fingerprints, hair, fibers, and other materials that serve as evidence linking the suspect to the crime scene or the victim. This theory underscores the importance of thorough crime scene investigations since every interaction could assist in reconstructing events or identifying participants.

The other options presented do not pertain to the concept of evidence transfer. Suicide risk deals with mental health assessments and interventions, inner perimeter theory is related to securing crime scenes, and mental health assessment references the evaluation of an individual's psychological state, which does not involve evidence left by physical interactions.