Impression Evidence - Forensic Science - Lecture Slides, Slides of Forensics

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Impression Evidence

Types of Impressions

 Patent (visible)—two dimensional impressions that are

visible to the unaided eye

 Prints in dust, blood, paint, etc…

 Latent – hidden to the eye but can be made visible using

development techniques

 Plastic—three dimensional imprints left in a soft substance

such as wax, snow, mud, etc…

 Can be easily lost so they must be made permanent through

casting

Definitions to remember

 Class versus individual evidence

Bite Marks

Permanent Teeth

 Gradually primary teeth are replaced by 32 permanent teeth.

 The last teeth to develop are the wisdom teeth which erupt

on average between 17-

 Teeth are a great indicator of age in children.

 The presence of wisdom teeth is an indicator that the

individual is over 17.

Bite marks

 Differences in the size of teeth and jaws, position and

crowding makes each person’s mouth unique.

 Can be used to:

 Identify remains

 Identify a suspect

Did you know? The most famous incident where bite mark evidence led to a conviction, was in the case of the notorious serial killer, Ted Bundy. He was responsible for an undetermined number of murders between 1973 and 1978 and was finally tied to the murder of Lisa Levy through bites that he had inflicted on her body.

Investigators can analyze bite marks for characteristics to help them identify victims or suspects as well as to exclude others. Marks can be left on a victim’s skin or other objects , such as Styrofoam cups, gum, or foods. Saliva or blood may be left behind that can be tested for DNA. Dental records including x-rays can also provide useful information, especially when attempting to identify a victim.

Features to analyze:

• Type of bite mark (human or animal)
• Characteristics of the teeth (position, evidence of dental work, wear patterns, etc.)
• Color of area to estimate how long ago the bite occurred (old or recent bite)
• Swab for body fluids for DNA tests

Bite Mark Evidence

Bite Mark Evidence Video

Tire Tracks

 The tread and impression are examined for two reasons:

 Tread pattern and measurements can be used to determine the

make and model of car

 Nature of the impressions can determine how the vehicle was

being driven

 Tire tracks can be patent, latent, or plastic

Anatomy of a tire

 The tread surface is made of ridges (elevations) and grooves

(indentations) which are designed to channel water away and

provide traction.

 Each model of tire has a unique pattern.

 A single tire tread can usually indicate the type of vehicle.

Identifying the Vehicle

 Because the same type of tire can be used on more than one

type of vehicle sometimes more information is needed.

 Track width is the distance from the center of the right tire

to the center of the left tire.

 May be different in front and back

 Wheelbase is the distance from the center of the front axle to

the center of the rear axle

 Turning diameter is the minimum space required for a car to

make a U-turn.

Turning diameter

Direction of travel

 Can be determined by:

 Vegetation that was disturbed

 Debris that was cast off

 Splash patterns from mud or water

 Substance transfer like an oil leak

 Tire marks

Tire Marks

 Skids

 Formed when you brake suddenly and lock the wheels.

 Provides evidence of when breaks wear applied

 Can calculate velocity using a

skid to stop formula