Locard’s principle is concerned:
Ref. Textbook of forensic medicine. Krishnan Vij. Page. 302
 
Locard Principle:

When any two objects come into contact, there is always a transfer of material from each object on the other.
Some examples are fingerprints, footprints,hair, tool marks etc.
Theory of relativity
Theory of decomposition
Theory of trauma
Theory of exchagnge
Theory of exchagnge