What is the 'exchange principle' of CSI?

What is the 'exchange principle' of CSI?

Richard Saferstein (Former Chief Forensic Scientist) gives expert video advice on: What is 'trace evidence' and how is it studied in CSI?; What is the 'exchange principle' of CSI?; How does studying hair help in CSI? and more...

The exchange principle came about as a result of the work of Edmond Locard who in 1915 founded the first crime lab in the world in Leone, France. He was very much interested in dealing with dust particles and items of trace evidence. He espoused the concept that every contact leaves a trace, and that gave rise to what we call The Locard Exchange Principle. That is the basic principle of underlined trace evidence analysis and trace evidence investigations today - every contact leaves a trace.