Shoeprint Casting Impression Evidence

Types of Prints Patent - visible print made by tracking through a substance such as paint or blood and leaving some behind Plastic - 3 D impression made by walking though mud, snow or something soft Latent - Invisible print made by the transfer of oil or grime from a substance to a hard surface such as a wooden floor or glass

Shoeprint impressions are generally class evidence. This means that they identify only the manufacturer and size of the shoe. To identify a particular person (individual evidence) you need to collect additional information from the print - –Pattern of wear based on how someone walks –Pattern of wear depending on kind of surface –Specific cuts, nicks, scratches and gouges

Shoeprints can also identify gait patterns Gait Walking style Length of stride Stance of person Estimate height, limp, odd walk

Patent prints Photographed head-on to reduce distortion Often with high-intensity light

Latent prints Usually deposited by shoes that are relatively clean Can be dusted with fingerprint powder, photographed or lifted with tape

Plastic prints Photographed with angled light to bring out detail Prints in snow or sand are first sprayed with dark spray paint Usually cast with dental stone - preferred because cast is harder and is easier to clean

Special situations When making a cast in soft mud or sand, the plaster can distort impression. Print is first sprayed with shellac or lacquer. Soil on cast is often saved for further analysis. Heat from the plaster melts a print in snow, so print must first be coated with snow print wax. Sometimes a print in carpet can be viewed with holography - image is recorded on film.

Plaster of Paris Chemistry Hemihydrate of calcium sulfate CaSO 4 ·1/2H 2 0 When mixed with water it produces gypsum CaSO 4 ·2H 2 0 Reaction is 2 CaSO 4 ·1/2H H 2 0  2 CaSO 4 ·2H heat