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Impressions and Toolmarks
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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
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
Footprint Evidence Characteristics
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Class characteristics are not unique,
however they can narrow the pool of possible
shoes:
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Size
Style
Tread pattern
Individual characteristics such as cuts,
cracks, embedded objects, and wear
patterns help to identify a specific shoe.
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 and angles
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 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
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
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
Introduction
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Tool mark—any impression, abrasion, or cut
made when contact occurs between a tool
and an object
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An example of physical evidence
Even mass-produced tools have minor
differences
The impressions can link the tool to a crime
scene and potentially to the owner
Forensic Science: Fundamentals & Investigations, Chapter 16
Tool Mark Impressions
Indentation Marks
o Result when a tool is pressed against a softer
surface
o Tools usually leave distinctive marks
o The hardness of a tool influences the
resulting marks left in the softer object
o May indicate the size of the tool used in a
crime
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Forensic Science: Fundamentals & Investigations, Chapter 16
Tool Mark Impressions
Abrasion Marks
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An object’s surface can be ground or worn
away by a tool
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The harder object causes abrasions on the
softer surface
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Indentation and abrasion marks sometimes
occur at the same time
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Forensic Science: Fundamentals & Investigations, Chapter 16
Tool Mark Impressions
Cutting Marks
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Edged instruments can penetrate a softer
object and separate it into parts
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Cut marks are produced along the edge as a
surface is cut
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Forensic Science: Fundamentals & Investigations, Chapter 16
Tool Mark Impressions
Examples of Cut Marks on Bones
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Forensic Science: Fundamentals & Investigations, Chapter 16
Documenting the Evidence
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Collect tool mark evidence when possible
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Photograph the evidence with a measuring
device to show scale
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Measure the size of the impression
Forensic Science: Fundamentals & Investigations, Chapter 16
Documenting the Evidence
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Castings preserve tool mark impressions
• silicone or rubber-based casting materials
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Cast impressions retain the unique
indentation marks made by a specific tool
Forensic Science: Fundamentals & Investigations, Chapter 16
Documenting the Evidence
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Dust for fingerprints before applying casting
material
• Use magnetic dusting powder and silicone material
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The size of the impression should be
measured and recorded.
Forensic Science: Fundamentals & Investigations, Chapter 16
Collecting and
Preserving a Sample
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Correctly label evidence
Wrap small objects with clean paper and
place them in small containers or plastic
bags
Pack large objects in cartons or boxes
Record—who, where, when, and why
Maintain the chain of custody
Forensic Science: Fundamentals & Investigations, Chapter 16
Analyzing Tool Mark Evidence
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Laboratory tool mark analysis identifies:
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major characteristics defining the type of tool used
in a crime
unique characteristics that might distinguish
between the same kinds of tools
Forensic comparison microscopes examine
tool mark characteristics that match a
suspect tool
Forensic Science: Fundamentals & Investigations, Chapter 16
New Technology in
Tool Mark Identification
Courts now require more than visual pattern
comparisons
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Tool mark databases (with images acquired by
forensic comparison microscopes)
Algorithms to statistically analyze tool mark
patterns
Scanning tools measure the depth or height of
tool marks
Forensic Science: Fundamentals & Investigations, Chapter 16
Tool Mark Evidence
in the Courtroom
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The tool mark witness prepares a written
report to present to a jury.
When available, provide:
• Original evidence
• Castings
• Magnified images of tool mark comparisons
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Such evidence may link a series of crimes
Forensic Science: Fundamentals & Investigations, Chapter 16