Tool Mark Impression Evidence Types of Impressions Patent

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 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.