When I was first introduced to crime scene investigation and studied all the aspects of forensic science, I gravitated toward impression evidence. At first glance, it doesn’t sound exciting. However, many cases have been solved by the simple, telling clues left behind from impression evidence.
A tire track left behind from a homicide or burglary.
A bit mark left on the victim or even on a piece of food.
A toolmark left from a screwdriver around a window opening.
Fingerprint impression left on duct tape found on a victim.
Gum spit out on the ground with a tooth impression left from a suspect.
Impression evidence is evidence left by anything that leaves a kind of impression at the scene or on an item, such as footprints, tire tracks, tooth impression, fabric indentations, or toolmarks. I find this type of evidence to be interesting and quite curious. It definitely tells a story.
For the forensic scientist, it’s not that they strictly compare the impression evidence to get a match, but rather, they establish individuality. It simply means that individualization is the uniqueness of a specific item of evidence. It has been described that no two fingerprints and snowflakes are exactly alike. The same holds true for gun barrels, show prints, pieces of broken glass, and lip impressions.
The simple principle of “all objects in the universe are unique” best explains impression evidence. Things can be similar of course, but that’s where class and individual characteristics comes onto play.
“No two things that happen by chance ever happen in the exactly the same way.
No two things are ever constructed or manufactured in exactly the same way.
No two things ever wear in exactly the same way.
No two things ever break in exactly the same way.”
Footprints are a valuable piece of impression evidence to any criminal case. They can be preserved from floors, outdoors, and anything that would adhere the shoe to give an impression on another surface.
Did you know that you can actually take castings of foot or tire impression in the snow?
The snow if first preserved by spraying a thin layer of a product called Snow Print Wax. Photographs should be taken before and after using this preservative. Then after this substance is allowed to completely dry, a casting of dental stone is poured into the area of the print. Dental stone should be made slightly thicker than normal and allowed to set up for at least an hour before removal.