Locard's Exchange Principle
Definition
The foundational idea that every contact between two surfaces moves material in both directions, giving the forensic process its starting premise: physical evidence exists because contact happened.
- Originator
- Edmond Locard (Lyon, 1910)
- Core concept
- Bidirectional transfer of material on any contact
- Foundation of
- All trace-evidence work in forensic science
Common questions
What is Locard's exchange principle?+
When two objects come into contact, material is transferred in both directions. It's the foundational axiom that physical evidence exists because contact happened, and it underpins all trace-evidence work in forensic science.
How does this principle apply to crime scenes?+
Every contact between two surfaces moves material in both directions. When two objects meet at a scene, material transfers both ways. This mutual transfer is what makes trace evidence discoverable and testable.
Who developed this principle and when?+
Edmond Locard, working in Lyon, formalized this principle in 1910. It remains the single load-bearing axiom that guides all trace-evidence work in forensic science today.
Related terms
- Anthropometry
- The measurement of the human body for scientific purposes. In forensic history, the Bertillon system of criminal anthropometry used eleven standardised body...
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- DFSS
- Directorate of Forensic Science Services, India; issues the Forensic Laboratory Manual that governs glass and soil examination procedures, including the bromoform-based density...
- Forensic Science
- The application of scientific methods and knowledge to questions that arise in legal proceedings. The goal is producing findings that are reliable,...
- NAS 2009
- US National Academy of Sciences report that found large parts of pattern-evidence forensics had no validated scientific basis. The reference point for...
- Physical Evidence
- Any tangible item or material that can help establish or disprove a fact relevant to a case. Distinguished from testimonial evidence by...
- Class Characteristic
- A feature shared by an entire group of objects (every shoe of one model has the same sole tread; every tire of...
- Class Characteristics
- Features deliberately or systematically imparted to a group of items by design or manufacture, such as the calibre of a bullet, the...
- Conditional Evidence
- Evidence whose meaning comes from the state or condition of a scene at the time of the crime, not from the physical...
- Control Sample
- A water sample collected from the suspected drowning environment at or shortly after the time of body recovery. Its diatom assemblage is...
- Corroborative Value
- Evidence that supports another piece of evidence without itself proving a fact. Most class evidence sits here.
- Crime Scene Management
- The organised approach to protecting, documenting, and processing a crime scene to maximise the recovery of physical evidence without introducing contamination or...
Explained in these topics
- Forensic Science: Definition, History, Scope and EthicsWhen two objects come into contact, material is transferred in both directions. The single most-tested principle in NET Paper 2.
- Forensic Science: Definition, Principles, History and EthicsWhen two objects come into contact, material is transferred in both directions. This is the single load-bearing axiom of the entire field.
- Physical Evidence: Types, Classification, Probative ValueEvery contact between two surfaces leaves a transfer in both directions. The 1910 maxim that underpins all trace-evidence work.
- Physical Evidence: Nature, Types, Collection and Chain of CustodyEdmond Locard (1910, Lyon): when two objects come into contact, there is a mutual transfer of material between them. The basis of all trace-evidence work.
- The Forensic Process: From Scene to CourtroomThe foundational idea that every contact between two surfaces moves material in both directions, giving the forensic process its starting premise: physical evi...