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