Locard’s exchange principle
A key principle that guides forensics is Locard’s exchange principle. Dr. Edmond Locard was a pioneer in the fields of forensics and criminalistics. His contributions to these fields led to many deeming him the Sherlock Holmes of France. His principle, simply put, is that every moment of contact with the physical world leaves a trace. For example, a burglar breaks a window to enter a home. They then crawl through this window and begin to grab the items around them. According to Locard’s exchange principle, the burglar will leave traces of dirt from their shoes on the carpet. Skin and hairs may fall away from their body onto the various surfaces of the home. Without gloves, the burglar might also leave fingerprints on the door handles.
This exchange is a two-way street. As our burglar leaves traces of themself around the house, traces of the house are left on them. Carpet fibers attach to their shoes. Fragments of the broken windows...
