Impression Analysis Tire Impressions Footwear Impressions Fabric Impressions

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