Locard's exchange principle

In my reading earlier this year, I ran across a 'transfer' and 'recovery' theory which I had not before encountered, called Locard's exchange principle. This theory was developed in the 1920s by French doctor Edmond Locard, who proposed "that when two objects come into contact with each other something is exchanged and taken away by both" (Oxford Reference, 2023. The exchange is today often named the 'silent witness' to crime, falling under the category of trace evidence. Dr Locard was the founder of the first forensic science laboratory in Paris, and was instrumental in professionalising fingerprinting  science (The Forensics Library, 2023). 

Our ability to detect the silent witness has come a long way in the past 100 years. We are now able to have blood traces re-emerge under ultra violet light with the addition of luminol. We can use DNA to - if not prove a link - at least to rule out links between suspects and victims. Microscopic fibres from a hug transfer from from one person's clothes to another's. Unusual pollen combinations can be tracked  from particular areas to a victim's lungs, and to a suspect's nasal hairs. Today it has become very complex for a suspect to avoid - or to remove - all trace evidence. 

Locard's exchange principle is - I presume - what drives shows like CSI and underpins many detective novels. The silent witness can today shout louder than ever. 

Sam

References:

Florida International University. (2013). Principles of Trace Evidence. Simplified Guide To Forensic Science. https://www.forensicsciencesimplified.org/trace/principles.html

Oxford Reference. (2023). Locard's Principle. https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100111515;jsessionid=6CAA47292E3F782E1A994BF4E1167CF6

The Forensics Library. (2023). Edmond Locard. http://aboutforensics.co.uk/edmond-locard/