Impression Analysis

Tire Impressions, Footwear Impressions, Fabric

Impressions, and Toolmarks

Shoe and Tire Impressions

• If shoe or tire is contaminated with blood, oil, or dust, it will leave a visible or latent print.– Visible prints are photographed– Latent prints are developed in a manner similar

to latent fingerprints.– Electrostatic technique – Plastic film is placed

over print and charged from a power supply, so that dust or powder is attracted to plastic.

• Impressions can also be plastic (3-D) in mud, snow, etc.

Locating and Casting Impressions

• Search for print in a manner similar to searching for fabric or glove prints.

• Plastic Prints are first photographed from directly above, and then a cast is made.

• Comparison prints are made by inking the soles of the shoes and placing them on an acetate sheet or tracing paper.

• First spray the impression with shellac or clear lacquer. Allow it to dry.

• Add retaining frame (2” depth)• Prepare casting material, and pour it in.• Before it dries, scratch in identifying material:

– Arrow indicating north– Case Number– Name of person preparing cast– Date

• Class characteristics– Manufacturer– Model– Size

• Individual Characteristics– Imperfections– Nicks, scratches, missing material.– Wear pattern– Foreign materials (rocks,etc.)

• NOTE: Impression may not be exactly the same size due to stretching of materials, etc.

• FBI Maintains database of tires and shoes for comparison

Fabric Prints

• Gloves– Visible or latent prints can be left due to

contamination• Should be developed, photographed, and

collected as if they were fingerprints– Plastic prints can be left in soft substances

• Cloth gloves – have snags, tears, or holes, as well as imperfections in weave pattern

• Leather Gloves – wrinkle or crease formations, surface cracks, tears, or imperfections

• Glove prints are less strong than fingerprints and may be destroyed by too much powder. Lifting may destroy the print.

• Comparison prints are made on glass

• Fabrics (clothing) can leave impressions (hit-and-run accident, for example) and should be treated the same way.

Tool marks

• Similar to firearms analysis• Implements used for cutting metal or prying

apart objects develop nicks on their edges with use.

• These nicks produce striations on items that are cut with the tool.

• Comparison marks are made on soft metals, such as lead

• Comparison microscope is used to compare tool mark impressions.– “comparative micrography”

• Cutting Tools (bolt or wire cutters)– Have a long blade– To avoid making numerous test cuts, chemical spot

tests are performed to see what part of the blade cut a particular metal.

• Hammer – leaves an impression (rather than striations) – like a pin impression