Exchange Principle | Edmond Locard

Edmond Locard formulated the single most important principle that has shaped the field of forensic science, namely the precept that “every contact leaves a trace”. It posits that in any encounter between bodies, objects, materials, and spaces certain residual traces are deposited and exchanged. These points of contact between entities can be mapped scientifically to link the distribution of bodies and objects within space. The Locard Exchange Principle reverses the classic model of cause and effect in that it is the effect that is subject to observation and the cause that is surmised or concluded.