Locard exchange of principle is
LOCARDS PRINCIPLE OF EXCHANGE: When any two objects come into contact, there is always a transfer of material from each object to the other. Traces from the scene may be carried away by the person and same traces from all or any of these may be left at the scene. Wherever a criminal goes whatever he touches and whatever he leaves will serve as silent evidence against him eg., fingerprints footprints, hair fiber from clothing, broken glasses, tool marks, paints scratch blood or seminal fluids, etc., It is actual evidence and its presence is absolute proof of the crime. REF: THE SYNOPSIS OF FORENSIC MEDICINE AND TOXICOLOGY 29th edition page no: 253.
Detecting poisoning
Estimating age
Finding out time since death
Detecting crime
Sexual offences and infanticide