Tires and shoes have one thing in common – they both leave patterns when they are used. A tire can leave a pattern in the dirt next to a house, or a shoe can leave a transfer of blood when a criminal leaves a crime scene. The patterns left by tires and shoes are often unique and can be examined to help investigators narrow the field of suspects.
Investigators look at 3 main characteristics when examining a pattern or imprint left by a shoe or tire: class, wear, and individual characteristics.
-Class characteristics: These are results from manufacturing. General class characteristics include the make and model of a tire, and limited involved the specific mold used to make a certain tire.
-Wear characteristics: As a shoe or tire is used more, more of it will change depending on how long it has been used. A tire 500 miles old will be very different from a tire that is 45,000 miles old. Shoes will wear differently based on how the owner walks and how long the shoes have been used.
-Individual characteristics: These are characteristics that are not a result of the manufacturing process. For example, if I stepped on a nail and it went through the bottom of my shoe, the mark left by the nail would be considered an individual characteristic.
According to Forensic Science Simplified, an accurate examination of a shoe or tire can give investigators clues such as “where the crime occurred, the number of parties or vehicles present, the direction a person may have traveled before, during, or after the crime, whether a person was on foot, and other crime scenes connected to a perpetrator.”
Prints are divided into 3 categories: visible (such as a blood shoe print), latent (not visible to the naked eye, such as a print on a sidewalk), and plastic (such a shoe print in the mud). Casting is often used to collect plastic prints, like a shoe print left in the mud. Lifting techniques can also be used – and there are several of those that can be used as well. These techniques include adhesive (adhesive is placed over a print commonly dusted with fingerprint powder then lifted off), gelatin (less sticky than an adhesive lifter, so it can be used without tearing fragile materials that a print may be on), and electrostatic lifting (particles are electrically charged and can then be attached to lifting film).
In this picture, investigators are inking a tire and driving over paper so that prints can be compared.
Investigators carefully examine any evidence they receive for clues to where it came from and who could have owned or wore the item that made a certain print. There are databases full of prints from tires and shoes that can be used to make comparisons. It is important that the examination is made precisely and carefully, or a valuable clue could be missed and a perpetrator could get away with a crime.
Source: “Footwear and Tire Track Examination.” Forensic Science Simplified. 2013. Web. 9 Apr. 2016.