<P> In forensic science, Locard's exchange principle holds that the perpetrator of a crime will bring something into the crime scene and leave with something from it, and that both can be used as forensic evidence . Dr. Edmond Locard (13 December 1877--4 May 1966) was a pioneer in forensic science who became known as the Sherlock Holmes of France . He formulated the basic principle of forensic science as: "Every contact leaves a trace". Paul L. Kirk expressed the principle as follows: </P> <Dl> <Dd> "Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him . Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects . All of these and more, bear mute witness against him . This is evidence that does not forget . It is not confused by the excitement of the moment . It is not absent because human witnesses are . It is factual evidence . Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent . Only human failure to find it, study and understand it, can diminish its value ." </Dd> </Dl>

Who stated that there is an exchange of materials when two objects come into contact with each other