revolver for shooting, poison for killing, pen for forging, and bodily force for committing other crimes against persons and property such as rape, murder, burglary etc. In the process, the criminal leaves marks such as fingerprint, foot prints, blood, seminal stains, saliva stains, fibers, tool marks etc., at the crime scene besides leaving behind minute bits of evidence at the crime scene, on the victim and on himself or herself.
However careful a criminal may be to avoid being seen or heard, he will inevitably defeat his purpose unless he can also control his every act and movement so as to prevent mutual contamination with his environment. Wherever he steps, whatever he touches, whatever he leaves even unconsciously will serve as silent evidence against him. However careful and conscious he may be avoiding leaving signs and traces of his presence or actions and whatever precautions he may take in destroying the evidence of his presence, he is bound to commit mistakes inadvertently which will stand against him.
But location of all such minute bits of evidence which may sometimes be invisible or partially visible is difficult to accomplish for the Investigation Officers without appropriate tools for identification, lifting and collection. But the fact remains that there do exist some interactive evidence all through the space the perpetrator traverses.