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Chapter 15
Cast and Impressions
By the end of this chapter you will be able to:
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Distinguish between patient, latent, and plastic
impressions
Describe how to make foot, shoe, and tire
impressions
Use track width and wheel base information to
identify vehicles
Prepare dental impressions and match them with
bite marks
All Rights Reserved South-Western / Cengage Learning © 2012, 2009
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Forensic Science: Fundamentals & Investigations, Chapter 15
What is impression evidence?
Impression evidence can be defined as objects or materials
that have retained the characteristics of other objects through
direct contact.
Impressions are created when one object is pressed
against another material with enough force to leave an
impression of the object.
Shoeprints, tool marks, tire tracks, bite marks, and
marks on a fired bullet are several examples of
impression evidence.
Impressions may be found in or on many different
types of materials. The quality of the impression
depends on the object making the impression and the
surface conditions, such as how hard or soft it is and
what type of material it is (soil, mud, dust, concrete,
grass, skin, etc.)
Images: http://upload.wikimedia.org/wikipedia/commons/archive/6/61/20070917141644!Shoeprint(forensic).jpg and
http://www.topmark.co.nz/images/content/tmpics01/gallery-s/SilipressionTeethMold.jpg
CSI &
Impressions
Introduction
People, vehicles, and
objects leave evidence
of their presence at an
accident or crime
scene.
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Patient impressions are two-dimensional
Latent impressions are hidden to the eye
Plastic impressions are three-dimensional
Forensic Science: Fundamentals & Investigations, Chapter 15
Collection Methods
Investigators analyze the impression evidence to find
unique characteristics to link shoes, tires, tools, and other
objects found in a suspect’s possession to evidence at a
crime scene.
Collection of impression evidence can be accomplished
using several methods:
2-D: This type of impression is documented using
photography. Some impressions may be dusted with
fingerprint powder to be photographed or lifted with tape.
They may also be collected using an electrostatic dust
lifting process.
3-D: This type of impression can be documented using
photography as well as by casting, which involves using
dental stone or a similar substance to preserve the
dimensional characteristics of the print.
Images: http://www.evidentcrimescene.com/cata/cast/dscasting.html
Shoe Print Evidence
Investigators can analyze a shoe print to determine its class,
or the type and brand of shoe. They will also look for
individual characteristics, such as wear patterns and
specific damages or defects.
Databases of shoe prints are available for investigators to
help them determine the brand of shoe to provide leads for a
case.
Depending on the quality of the impression, investigators
may be able to determine a person’s speed (walking vs.
running) as well as estimate the size of a person based on the
impression’s depth.
Features to analyze:
• Tread patterns, size, and depth
• Wear patterns caused by the way a person walks
• Material defects or damage (nicks, cuts, etc.)
• Other trace materials, such as soil, tar, rocks, and paint
that would indicate where a person has been
Images: http://www.stampmatch.com/results.html and
http://www.fosterfreeman.com/products/shoeprints/solemate/solemate.html
STAMP Database
Shoe Print in Bio-Foam
Impression Foam
Shoe Impressions
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Shoeprint 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 walks
Unique holes, cuts, and debris embedded in
the tread
Forensic Science: Fundamentals & Investigations, Chapter 15
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
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Forensic Science: Fundamentals & Investigations, Chapter 15
Lifting Latent Impressions
Different methods to make latent prints visible:
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Luminol makes bloody footprints visible for
photography
Dusting the latent print reveals an impression for
lifting or photography
Electrostatic lifting and gel lifting (image below)
techniques can capture hidden impressions
Forensic Science: Fundamentals & Investigations, Chapter 15
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
Comparing Shoe Size and Height
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Forensic Science: Fundamentals & Investigations, Chapter 15
Tire Track Evidence
Tire tracks are important in forensic investigations and are
usually found in road accident scenes or in the access and
escape routes of other crime scenes. Tracks help
investigators identify the type of vehicle that left them.
Investigators may make ink prints of a tire or plaster
casts of a track. They will also take photographs that can
later be used to prove a match.
Features to analyze:
• Tread pattern
• Width & depth of the tread pattern
•Unique characteristics due to the wear pattern or defects
Tire databases are available help investigators
determine the brand and model of the tire that
left the impression , which can be used to
determine the type of vehicle that made the
tracks.
Images: http://www.suite101.com/view_image.cfm/454216, http://www.ronsmithandassociates.com/FWTTS.htm.
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
Tire Treads and Impressions
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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
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
Identifying a Vehicle
Track widths—
From center of tire to center of tire
Wheelbase length—
From center of front axle to center of rear axle
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Forensic Science: Fundamentals & Investigations, Chapter 15
Identifying a Vehicle
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Turning diameter
Databases can be
checked to find the
vehicle with these
specifications
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Forensic Science: Fundamentals & Investigations, Chapter 15
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
There are three basic types of tire marks:
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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
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Tire scrub—determines the area of impact
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How are each of these formed?
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Forensic Science: Fundamentals & Investigations, Chapter 15
Bite Mark Evidence
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.
Bite Mark Evidence Video
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
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.
Images: http://www.forensicdentistryonline.org/Forensic_pages_1/currentopic1.htm, http://www.trestonedental.co.uk/images/0303.jpg
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
Development of Teeth
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Forensic Science: Fundamentals & Investigations, Chapter 15
Dental Patterns in Forensics
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The investigation consists of recognizing, documenting, collecting, and analyzing evidence
What are the two basic ways dental patterns can
be used in forensic investigations?
There are 76 points of comparison when comparing a
suspect’s dental patterns with bite marks left at a
crime scene
What is the common method used to reveal
whether there is a match?
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Forensic Science: Fundamentals & Investigations, Chapter 15
. . . . . . . . . . . . . . . . . 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