Tool Mark & Impression Evidence

Types of Impressions Patent Impressions – two dimensional, visible impressions Latent Impressions – impressions that are hidden to the naked eye Plastic Impressions – three-dimensional impressions

Shoe Impressions Can provide information such as height of the individual, how someone moves, and identify other crime scenes Databases contain the names of specific manufacturers and tread patterns that can be used to identify different types of shoes.

Shoe Wear Patterns Some factors that personalize a person’s footwear include: - Body weight - The way a person walks (gait) - The surface on which the person usually walks. - Debris that became embedded in the tread or unique holes and cuts in the tread.

Lifting Impression Evidence Latent Impressions: Luminol for bloody prints Electrostatic lifting

Patent Impressions: Very complete photographic evidence collection is necessary for most patent impressions as they often cannot be saved.

Plastic impressions can be lifted using plaster or dental stone.

Tire Impressions Can be lifted from dirt, snow, sand and even standing water. Lifted using various substances including plaster of paris, dental stone, sulfur, snow-print wax Can leave patent, latent, or plastic tread patterns.

Tread Impressions Ridges and grooves of discovered impressions are counted across the entire width. Unique characteristics such as wear or pebbles embedded in the grooves are noted A print of a suspect’s tire impression through one full revolution is taken

Identifying Characteristics Front and Rear Track Width – measured from the center of each tire to the center of the opposite tire.

Wheelbase – the distance between the enter of the front axle to the center of the rear axle.

Turning diameter – the distance required for a car to make a U-turn (1/2 of circle).

Accident Reconstruction There are three basic types of tire marks: Skid Marks – forms when someone brakes suddenly and locks the wheels.

Yaw Marks- produced when a vehicle travels in a curved path faster than the vehicle can handle and skids sideways.

Tire Scrub - produced by a damaged or overloaded tire or tires during or immediately after impact.

Dental Impressions Like fingerprints, dental impressions are usually considered individual evidence.

Factors that affect our dental impressions include: Number of teeth/Missing teeth Coloration of teeth Size of teeth Alignment of teeth and distance between teeth Unique fillings, crowns, caps Overall condition of teeth (breakage/chipped teeth, grinded teeth etc…)

Structure of Teeth

Bite Mark Comparisons Up to 76 points of comparison Places where locations on bite where impressions are often detailed Comparison includes: Dental chipping, surface indentations, distances between teeth, alignment of teeth, angle of mouth arch, absence of teeth Bite mark should be photographed with ruler included as soon as possible Bite mark should be swabbed, may contain DNA from saliva

Tool Marks Tool Marks are any impression, abrasion, or cut made when contact occurs between a tool and an object. Even mass-produced tools have minor differences.

Indentation Marks Indentation marks – made when a tool is pressed against a softer surface.

Abrasion Marks Abrasion Marks – made when surfaces slide across one another.

Cut Marks Cut marks are produced along the edge as a surface is cut.

Tool Mark Analysis Usually done with a comparison microscope.