Impressions

Categories of Impressions Patent impressions – visible, two-dimensional impressions produced as an object moves through soil, dust, paint, blood, etc., and leaves a trace Latent impressions – hidden to the eye but can be visualized through special dusting and electrostatic techniques or chemicals Plastic impressions – three dimensional imprints left in soft material such as snow, mud, soil, soap, etc. May be easily lost due to changing weather

Shoe Impressions may be class evidence or individual evidence (tread pattern is class evidence, unusual wear on the tread is individual evidence) Shoeprints can help police determine size of person’s foot, weight, type of shoe (could give info about profession), brand of shoe (could give info about financial status)

Shoe Databases Contains information regarding specific manufacturers and tread patterns that help identify different shoes

Shoe Wear Patterns Shoes become personalized with each wearer’s own characteristic way of walking. Some factors include: Whether a person walks on their heels or toes Body weight If the person walks straight ahead or with toes pointed inward or outward Shape of the foot and the wearer’s activities Surface on which the person usually walks Unique holes, cuts or debris that may be embedded in the shoe

Gait and Tracks numerous prints tell about the person’s gait, or walking habits An asymmetrical gait may indicate a limp or someone carrying a heavy weight Length of stride (space between tracks) indicates if someone was walking or running More Information that can be obtained Number of people at the crime scene Movement of individuals at the scene (did the crime happen in one room or several rooms) Entrance and exit to the crime scene

Collection of Shoe Impression Evidence 1. Photographing evidence Take photos before anyone touches or alters an impression Fill the camera’s viewfinder with the impression Take photos with the lens perpendicular to the impression (reduces distortion) Take multiple photos from at least two different angles Use film vs digital photos (so photo is not altered) Place an identifying label and a ruler in position with the impression and rephotograph

Collection of Shoe Impression Evidence (continued) 2. Lifting Latent Impressions Make the latent print visible by using Luminol – allows bloody footprints to become visible and photographed Dusting – similar to dusting for fingerprints. This reveals the impression and makes it visible to be photographed and lifted. Electrostatic Dusting – applies an electric charge on a piece of lifting film which is placed over the latent print and allows the dust from the latent print to be picked up Gel Lifting – gel layer that is flexible and can conform to uneven surfaces…print is dusted with powder, the gel is placed on top and the powder print comes off on the gel

Collection of Shoe Impression Evidence (continued) 3. Casting Plastic Impressions Cast – a three dimensional impression in mud or snow. Casting material depends on the conditions… Plaster of Paris is used in sand or dirt, dental stone is used in snow (doesn’t generate heat so the snow print won’t melt)

Foot Length & Shoe Size size of a shoe varies by shoe type...a running shoe gives a much smaller impressions than a steel-toed work boot of the same size A person’s height is generally related to their foot size, but it is impossible to predict someone’s exact height from their foot size