tool marks and impressions

Tool Marks and ImpressionsTool Marks and Impressions


• A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming in contact with another object.

• A “tool mark” can be caused by an endless list of objects:

• A screwdriver is most often used to tighten or loosen screws.However, if it is used to pry open a widow it will leave impressionsIn the window sill.

Examples:

• Car tires leave impressions in the ground.

• Even a button on your shirt will leave an impression on your skinif pressed hard enough.


• Tool marks come in two general categories:

• Compression Marks • Scraping Marks


• In general tool marks reveal class characteristics, such as sizeand shape of tool used.

• However, once a tool has been used minute random markings on thesurface can impart individual characteristics to objects.


• Footprint impressions are useful information when collected at acrime scene.

Footprints

• Initially shoe prints are classified as class evidence. However, over time all shoes acquire their own wear pattern, nicks, markings,etc.

• Once a shoe has been worn for a period of time, it becomes unique,and it then becomes individualized.

http://www.irlab.com/quinsee/images/ShoePrint.gif

http://www.irlab.com/quinsee/images/ShoePrint.gif


Bloody Shoe Print


• Footprints made in the ground can be cast with plaster and usedfor comparison.

Tool Marks and ImpressionsTool Marks and ImpressionsTires

• Tire tread impressions and prints can be useful evidence left at acrime scene.

• As in any mass produced item, initially a new tire will exhibit classcharacteristics.

• However, in time the tire will acquire a unique wear pattern makingeach tire individual.


• Dimensions left by tire marks or impressions are helpful in identifyinga particular vehicle.

Tread Width – the distance across tread pattern.

• Typically larger trucks and SUV’s have larger tires than compact cars.


• Tire marks can also indicate a vehicles direction of travel.

• When a vehicle is traveling in a straight line, the rear tires travelover the prints made by the front tires.

• Therefore, a turn is the best place to see clear prints.

Tool Marks and ImpressionsTool Marks and Impressions• Describe how this car was traveling.

Front TiresForward

Rear TiresForward

Rear Tires Reverse

Front TiresReverse

Rear Tires Forward Again

Front TiresForward Again

Tool Marks and ImpressionsTool Marks and ImpressionsBite marks

• Bite marks left on skin can leave impressions which can be tracedback to suspect.

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tool marks and impressions

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