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5/5/2015
Chapter 15
Cast and Impressions
By the end of this chapter you will be able to:
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Distinguish between patent, latent, and plastic
impressions
Describe how to make foot, shoe, and tire
impressions
Use track width and wheelbase information to
identify vehicles
Explain dental impressions and match them with
bite marks
Forensic Science: Fundamentals & Investigations, Chapter 15
O.J Simpson-If it doesn’t fit, you
must acquit
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OJ Simpson’s Bruno Magali Shoes
OJ Simpson’s Bruno Magali
Shoes
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Cast and Impressions
Evidence in the form of impressions is
often found at the scene of a crime.
there are three kinds of impressions:
latent, patent, and plastic.
Each kind of impression tells an
important part of what happened at
the scene of the crime.
Cast and Impressions
● Foot, shoe, dental and tire impressions
can be collected.
● From tire tracks, investigators can
establish information to identify a
vehicle
● Teeth impressions are as individual as
fingerprints
● Shoe impressions can establish body
weight, wearer’s activities and surfaces
that the suspect usually walks on
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Casts and Impressions
People, vehicles,
and objects leave
evidence of their
presence at an
accident or crime
scene.
o
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Patent impressions are two-dimensional
Latent impressions are hidden to the eye
Plastic impressions are three-dimensional
Forensic Science: Fundamentals & Investigations, Chapter 15
Patent Impressions
● Patent prints are 2 dimensional
impressions that are visible to the
human eye. They are from foreign
substances that are transferred to
another surface
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Latent Impressions
Latent Impressions are left by blood, oils
and sweat from the skin and transferred
onto smooth surfaces. However, they
are invisible to the naked eye and are
recovered using alternate substances
Plastic Impressions
Plastic impressions are 3 dimensional
imprints that can be left in soft
materials, such as: snow, mud, soil, or
soap
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Individual or Class Evidence?
o Depending on how an impression is
made determines whether if it is
individual or class evidence
o A particular tread pattern in shoes or
in tires may identify the brand and
size, but it does not identify a
specific individual
Individual or Class Evidence?
Distinguishing characteristics such as: a
split on a shoe sole or an unusual wear
pattern on a car tire could be used as
individual evidence
Dental impressions are typically considered
individual evidence and have a long history
of use to identify individuals
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Shoe Impressions
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Shoe print size indicates the foot size
The depth of a foot or shoe impression
indicates a person’s weight
The type of shoe can tell something of the
person’s job or personality
Databases contain the names of specific
manufactures and tread designs
Forensic Science: Fundamentals & Investigations, Chapter 15
Shoe Wear Patterns
Factors that personalize a person’s footwear:
o Body weight
o The way a person walks
• Weight distribution
• Direction of toes (straight, pointing out or in)
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The surface on which the person usually
walks
Unique holes, cuts, and debris embedded in
the tread
Forensic Science: Fundamentals & Investigations, Chapter 15
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Shoe Wear Patterns
Databases contain the names of specific shoe
manufacturers and tread patterns used to identify different
types of shoes
Collection of
Shoe Impression Evidence
Why would the following steps be important?
1. Take photos as soon as possible
2. Take multiple photos of the impression from
at least two different orientations
3. Place an identifying label and a ruler in
position with the impression for the photo
4. Use oblique lighting when possible
5. Dental stone is used to cast shoe prints
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Forensic Science: Fundamentals & Investigations, Chapter 15
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Casting Shoe Impressions
https://www.youtube.com/watch?v=mq
uyNZaNbPo
http://www.ncbi.nlm.nih.gov/pubmed/
19767544
Comparison of male/female feet
Lifting Latent Impressions
Different methods to make latent prints visible:
o
Luminol makes bloody footprints visible
for photography
o Dusting the latent print reveals an
impression for lifting or photography
o Electrostatic lifting and gel lifting (image
below) techniques can capture hidden
impressions
*
Forensic Science: Fundamentals & Investigations, Chapter 15
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Electrostatic lifting
https://www.youtube.com/watch?v=jQz4gNjcvAA
Electrostatic Dusting
and Lifting
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Electrostatic dusting reveals dust left with each
step and creates an impression
Electrostatic charges can lift impressions from
paper
wood surfaces
carpeting
linoleum
asphalt
concrete
Gel lifters also recover latent impressions
Forensic Science: Fundamentals & Investigations, Chapter 15
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Comparing Shoe Size and Height
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Forensic Science: Fundamentals & Investigations, Chapter 15
Tire Treads and Impressions
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Tire treads—ridges and grooves channel water
away and provide traction
Patent tread patterns—impressions made after
tire runs through a fluid material
Latent tread patterns—impressions from tire
oils used to keep tires soft and pliable
Plastic tread patterns—three dimensional
impressions left in soft surfaces
Forensic Science: Fundamentals & Investigations, Chapter 15
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Tire Treads and Impressions
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Unique design of a tire’s surface is referred to
as a tread pattern
Tread patterns can indicate the type of vehicle
that left the mark
Link a suspect or victim to a crime scene
Reveal events that took place at the scene
Forensic Science: Fundamentals & Investigations, Chapter 15
Anatomy of a Tire
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Forensic Science: Fundamentals & Investigations, Chapter 15
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Tire Tread Design
https://www.youtube.com/watch?v=Hv
NzsqvQbS8
Recording Tread Impressions
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Count ridges and grooves across the tire width
Note unique characteristics—wear or pebbles
embedded in the grooves
Create a print of the suspect’s tire impressions
through one revolution
Compare impressions from the crime scene and
suspect’s tire
Identifying tread patterns may not be enough to
link a suspect with a crime scene
Forensic Science: Fundamentals & Investigations, Chapter 15
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Identifying a Vehicle
Track widths— (Side view)
From center of tire to center of tire
Wheelbase length—(Front view)
From center of front axle to center of rear axle
*
Forensic Science: Fundamentals & Investigations, Chapter 15
Identifying a Vehicle
o
Turning diameter is a measure of how tight of a
circle can be driven by a vehicle or the minimal
space required for a car to make a U-turn
Databases can be
checked to find the
vehicle with these
specifications
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Forensic Science: Fundamentals & Investigations, Chapter 15
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Accident Reconstruction
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Drivers may not recall the exact series of events
before, during, and after an accident
People, vehicles, and objects, however, can leave
evidence of their actions at the scene of an accident
Debris patterns and tire marks can be clues to speed,
direction, and vehicle identification
Forensic Science: Fundamentals & Investigations, Chapter 15
Accident Reconstruction
https://www.youtube.com/watch?v=u96_C
gE86ys
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Accident Reconstruction
There are three basic types of tire marks:
o
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Skid marks—clues to the distance traveled after brakes
are applied and the vehicle’s speed
Yaw marks—shows a sideways skid
Tire scrub—determines the area of impact
How are each of these formed?
*
Forensic Science: Fundamentals & Investigations, Chapter 15
Dental Impressions
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Occasionally a perpetrator will leave behind a bite
mark—considered individual evidence
Note differences in the size of teeth and jaws,
position, fillings, crowns, caps, breakage, and
crowding
Forensic Science: Fundamentals & Investigations, Chapter 15
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Development of Teeth
● The appearance of teeth follows a
predictable pattern beginning in the first
7-12 months of life
*
Forensic Science: Fundamentals & Investigations, Chapter 15
Development of Teeth
● Gradually, the primary teeth are
replaced by 32 permanent teeth
● The last teeth to emerge are the wisdom
teeth, which emerge between 17 and 21
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Dental Patterns in Forensics
There are the two basic ways dental patterns
can be used in forensic investigations:
1. Used to identify unknown bodily remains,
and;
2. identifying a suspect from a unique bite
pattern or bite marks left at the scene of a
crime
*
Forensic Science: Fundamentals & Investigations, Chapter 15
Dental Patterns in Forensics
o There are 76 points of comparison when
comparing a suspect’s dental patterns with
bite marks left at a crime scene, such as:
-Chipping, missing teeth, space
between teeth, teeth alignment,
individual tooth dimensions, etc..
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. . . . . . . . . . . . . . . . . Summary
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Impression evidence—whether patent, latent, or
plastic—will be considered class evidence unless it
has individualizing features.
Debris patterns and tire marks can be clues to speed,
direction, and vehicle identification.
Differences in dental patterns can connect a person to
a crime scene.
Documentation (including early photos) is extremely
important in an investigation.
Forensic Science: Fundamentals & Investigations, Chapter 15
Always leave a good impression
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