What is the name of the principle that says: Anyone or anything entering a crime/incident scene takes something with them and leaves something of them behind when they depart?

The principle that states, "Anyone or anything entering a crime/incident scene takes something with them and leaves something of them behind when they depart," is known as Locard's Principle. This principle is fundamental in forensic science and criminal investigation, highlighting the inevitability of exchange during interactions. In practice, it suggests that every crime scene reflects traces of the perpetrator, such as fingerprints, hair, fibers, or other materials, along with any artifacts or materials that the offender may carry away with them.

Locard's Principle emphasizes the importance of meticulous evidence collection and examination, reinforcing the idea that investigation techniques must focus on both what is left behind and what may have been taken away. This principle is a cornerstone of forensic methodology, facilitating the connection between a suspect and a crime scene. It serves as a guideline for forensic examiners when they analyze physical evidence and try to reconstruct events surrounding a crime.