Is there any validity to the notion that criminals leave something behind at the scene and take something away from the scene? Give examples.
In theory, this is true. Consider the number of ways a criminal can leave information behind. Such obvious things can be left behind such as fingerprints. These can now be retrieved from a number sources including some that were previously impossible, such as skin. Dirt can sometimes be carried in on the criminal’s shoes and matched to specific regions. Hair can be shed at the scene of a crime, and if the follicle is attached, DNA can be retrieved. Smaller items such as saliva and epithelial cells are left behind. Now whether these are found in evidence collection or whether they can be matched in any usable way is sometime uncertain. The criminal might pick up epithelial cells, hair, dirt, and other items from the victim, and these can later be traced back to the victim. Key in all of this is probably going to be technology that keeps improving, and making it easier for crime scene investigators to do their jobs.