Three examples of how evidence may be destroyed by onlookers at a crime scene are these:
1) Onlookers may walk through the crime scene that may
destroy the footprints of the criminal or the victim.
2) Onlookers may enter the crime scene and touch some item
which will result in destroying the fingerprints found there.
3) Onlookers may touch, take, move around or change an object
from the crime scene contaminating / destroying any fibers or hair which may
come handy during investigation.
