Edmond Locard’s Exchange Principle

Yash Gorasiya
4 min readDec 30, 2020

Forensic science involves Forensics which means public discussion or debate.
Forensics applies to courts or the judicial system. Combining forensics with science helps in applying scientific method to solve the crimes. Forensic science is the application of science to criminal and civil laws mainly- on the criminal side during criminal investigation, as governed by the legal standards of admissible evidence and criminal procedure. Forensic science applies science principles, techniques and methods to the investigation of crime. Forensic science involves a multidisciplinary approach that covers everything from biological methods to analytical chemistry techniques.

After 1900’s there was a Drastic change in the field of Forensic chemistry . During this time there came several new techniques and Principles which later on helped or are considered as the most important during an Investigation. One Among them was the Edmond Locard’s Exchange Principle .

Dr. Edmond Locard (13 December 1877–4 May 1966) was a French criminologist, the pioneer in Forensic Science who became known as the “Sherlock Holmes of France”. In 1910, Locard succeeded in persuading the Police Department of Lyon to give him two attic rooms and two assistants, to start what became the first Police Laboratory .

Locard’s work formed the basis for what is widely regarded as a cornerstone of the forensic sciences, Locard’s Exchange Principle given in 1910 , which states that “ with contact between two items, there will be an exchange ”. It was Locard’s assertion that when any person comes into contact with an object or another person, a cross-transfer of Physical Evidence occurs. By recognizing, documenting, and examining the nature and extent of this evidentiary exchange, Locard observed that criminals could be associated with particular locations, items of evidence , and victims. The detection of the exchanged materials is interpreted to mean that the two objects were in contact. This is the cause and effect principle reversed; the effect is observed and the cause is concluded.

Locard, however, did write the following: “It is impossible for a criminal to act, especially considering the intensity of a crime, without leaving traces of this presence.” In other words, Locard believed that no matter where a criminal goes or what a criminal does, he will leave something at the scene of the crime. At the same time, he will also take something back with him. A criminal can leave all sorts of evidence, including fingerprints , footprints, hair, skin, blood , bodily fluids, pieces of clothing and more. By coming into contact with things at a crime scene, a criminal also takes part of that scene with him, whether it’s dirt, hair or any other type of trace evidence.

The following are the cases when Locard’s Principle was used in the Initial Days . Then from their it gained popularity.

  • Locard’s techniques proved useful to the French Secret Service during WORLD WAR I (1914–1918), when Locard was able to determine where soldiers and prisoners had died by examining the stains on their uniforms.
  • Dr. Locard tested out this principle during many of his investigations. In 1912, for instance, a Frenchwoman named Marie Latelle was found dead in her parents’ home. Her boyfriend at the time, Emile Gourbin, was questioned by police, but he claimed he had been playing cards with some friends the night of the murder. After the friends were questioned, Gourbin appeared to be telling the truth. When Locard looked at the corpse, however, he was led to believe otherwise. He first examined Latelle’s body and found clear evidence that she was strangled to death. He then scraped underneath Gourbin’s fingernails for skin cell samples and later viewed the results underneath a microscope . Very soon, Locard noticed a pink dust among the samples, which he figured to be ladies makeup. Although makeup was popular around the time of the murder, it was by no means mass produced, and this was reason enough for Locard to search a little further. He eventually located a chemist who developed a custom powder for Latelle, and a match was made. Gourbin confessed the murder — he had tricked his friends into believing his alibi by setting the clock in the game room ahead. Locard’s exchange principle had worked.

This was some key points regarding the Locard’s Principle which everyone must be aware of . Coming up with the Two case studies Based on Locard’s Principles . Till then Happy Learning !!



Yash Gorasiya

Associate Project Manager at The SecOps Group || Technical Writer at The SecOps Group || Cyber Security Writer at VulnMachines