IMPRESSION EVIDENCE - LHS SCIENCE -...
Transcript of IMPRESSION EVIDENCE - LHS SCIENCE -...
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IMPRESSION EVIDENCE
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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
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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
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• 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.
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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.
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Shoes & Shoeprints
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2-D Footwear
3-D Footwear
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Accidentals
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Elimination Prints
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• 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
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Negative Impression
Positive Impression
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Tread Elements
(Footwear)
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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
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Known Impressions
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Class
Characteristics:
•Tread Design
•Size of Tread
CAN’T be used to
individualize
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Photo of Suspect’s Shoe
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Q K
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Known
Impression
Questioned
Impression
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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
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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
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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.
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Other Prints
• Palm - friction ridges can
be identified and may be
used against suspects
• Lips—display several
common patterns
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Other Prints
• Footprints
–size of foot and toes;
friction ridges on the
foot
–Taken at birth as a
means of identification
of infants
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Other Prints
Ears—shape, length and width
Voice—electronic pulses
measured on a spectrograph
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Other Prints
The blood vessel
patterns in the eye
may be unique to
individuals. They are
used today for various
security purposes.