impression evidence - lhs science -...

IMPRESSION EVIDENCE

Terminology• 2-D (two dimensional) Impressions – impressions with two

dimensions (length and width) such as impressions in dust, blood, etc. on a hard surface

• 3-D (three dimensional) Impressions – impressions with three dimensions (length, width, and depth) such as impressions in dirt or snow that have depth

• Accidental/Unique Characteristics – cuts, scratches, and other damage which can be used to individualize a shoe to an impression

• Elimination Prints – Known print

– Ex: Photos of the bottoms of the shoes of all personnel that enter the crime scene

• Latent Impression – an impression that is invisible without some type of enhancement or oblique lighting

• Partial Impression – an incomplete impression that only has a portion of the overall tread design present

Bite Marks/Teeth Impressions• Universal system - A number is assigned to

each of the thirty-two adult teeth, beginning at

#1 with the upper right third molar and ending

with the lower right third molar

• Teeth are tools and a tooth mark is like a tool

mark.

– teeth that leave the strongest impressions

are in the front, both top and bottom

– chip, get worn down, or be reshaped in

various ways

– restorations, fillings, rotations, tooth loss,

breakage, and injury that can make one

person's teeth unlike anyone else's

• Sometimes a bite-mark has to be charted and

examined from many angles; sometimes it can

be identified from one tooth

• Bite marks left on foodstuff, such as cheese or gum, offer a three-

dimensional impression, which is superior to the two-dimensional

impression often left on skin.

• A bite might penetrate the skin, but often only leaves bruising

– sometimes the blood marks of a bruise are mistaken for the

impression of a tooth.

– skin gets distorted when bitten, or the teeth slide during the act of

biting.

– Some bites are forceful enough to leave a good impression, others

are not.

The physical characteristics of both the bite mark wound and the suspect's

teeth include:

-the distance from cuspid to cuspid

-the shape of the mouth arch

-the evidence of a tooth out of alignment

-teeth width and thickness, spacing between teeth

-missing teeth

-the curves of biting edges

-unique dentistry

-wear patterns such as chips or grinding.

Case Example

• Bundy's teeth and

bite marks on Lisa

Levy

(trial evidence)

• The tissue from Lisa Levy's

buttock had been destroyed

in all the analyses, but the

photograph with the ruler

still remained.

• Pointed out how unique the

indentation mark was and

showed how it matched the

dental impressions of

Bundy's teeth.

• First case in Florida's legal

history that relied on bite-

mark testimony, and the

first time that a physical

piece of evidence actually

linked Bundy with one of his

crimes.

Shoes & Shoeprints

2-D Footwear

3-D Footwear

Accidentals

Elimination Prints

• Negative Impression – impression created by shoe treads coming into contact with a dirty surface and taking dirt/dust away (areas where the shoe made contact are clean with dirt/dust around them)

• Oblique Lighting (side lighting) – lighting at an angle with respect to the impression (usually approximately 30 to 45 degree angel for 3D impressions and 10 degrees to parallel with the floor for 2D impressions)

• Positive Impression – impression created by dirt or other residue on the shoe treads that is left behind on a surface (areas of a floor where the shoe made contact are soiled by dirt or other substance that was adhering to the bottom of the shoe)

• Tread Element – the individual treads that make up a tread design of a shoe or tire

• Wear Characteristics – As the a shoe is worn, the tread elements wear down and can change their shape or texture

Footwear Terminology

Negative Impression

Positive Impression

Tread Elements

(Footwear)

Footwear Comparison

Tread Design (class character)

Size of Tread Design (class character)

Wear Characteristics (unique)

Accidental or Unique Characteristics

(unique)

Can be as individual as a fingerprint

Must have shoes to make a positive ID

Known Impressions

Class

Characteristics:

•Tread Design

•Size of Tread

CAN’T be used to

individualize

Photo of Suspect’s Shoe

Q K

Known

Impression

Questioned

Impression

Comparison Results

• If the shoes are dissimilar in tread design, the shoe is ELIMINATED

• If the shoe has same tread design, but different size it is also ELIMINATED

• If the shoe has similar tread design and size, the shoe COULD HAVE made the impression

• If the shoe has similar tread design, size, and a couple of accidentals (but not enough for positive ID), the shoe LIKELY made the impression

• If Similar tread design, size, and enough accidentals, it is a POSITIVE ID

How Many Accidentals?

• No specific number required for positive ID

• Based on experience of the examiner, types

of accidentals present and how clear the

accidentals are in the questioned

impressions

• Accidentals have different

weights/significance depending on shape

and size

Tire Tread

• record and analyze impressions of vehicle

tire treads

• Initially can tell the brand of tire

• every tire will show different amounts of

tread wear & different amounts of damage

– tiny cuts and nicks

– defects and wear caused by nails, gravel,

patches and alignment problems

• unique characteristics will show on the

impression left by the tire.

Other Prints

• Palm - friction ridges can

be identified and may be

used against suspects

• Lips—display several

common patterns

Other Prints

• Footprints

–size of foot and toes;

friction ridges on the

foot

–Taken at birth as a

means of identification

of infants

Other Prints

Ears—shape, length and width

Voice—electronic pulses

measured on a spectrograph

Other Prints

The blood vessel

patterns in the eye

may be unique to

individuals. They are

used today for various

security purposes.