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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Exchange of trace evidence occurs, When a person comes in contact with other person . This principle is called?
assistant
The correct answer is  Locard's principle of Exchange 

It States that " When two objects come into contact with each other, there is always transfer of some material between them".
This is helpful in crime investigations, especially in sexual offences.