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Toolmark Identification
Toolmark
Identification
n
Toolmark Identification - a discipline of
forensic science which has as its primary
concern to determine if a toolmark was
produced by a particular tool.*
* Association of Firearm and Tool Mark Examiners Glossary 4th Edition
Toolmarks - Definitions
Tools
n
Tool – An object used to
gain mechanical
advantage. Also thought
of as the harder of two
objects which when
brought into contact with
each other, results in the
softer one being
marked.*
* Association of Firearm and Tool Mark Examiners Glossary 4th Edition
© Precision Forensic Testing
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© Precision Forensic Testing
When examining toolmarks, there are two types of characteristics to
consider. The first is class characteristics.
Class characteristics are measurable features of a specimen which
indicate a restricted group source. They result from design factors,
and are therefore determined prior to manufacture.*
The second type of characteristic to examine when evaluating
toolmarks are individual characteristics.
Individual characteristics are marks produced by the random
imperfections or irregularities of tool surfaces. These random
imperfections or irregularities are produced incidental to
manufacture and/or caused by use, corrosion, or damage. They are
unique to that tool and distinguish it from all other tools.*
* Association of Firearm and Tool Mark Examiners Glossary 4th Edition
© Precision Forensic Testing
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Locking Pliers
Tools - Types
n
When discussing types of tools, we can classify them
based on their design. Examples of these tools
include:
§ Locking Pliers
§ Needle Nose Locking Pliers
§ Slip Joint Pliers
§ Tongue and Groove Pliers
§ Linemans Pliers
§ Diagonal Cutters
§ Wire Cutters/Strippers
§ Pipe Wrenches
§ Circular Cutting Tools
§ Chisels
§ Screwdrivers
§ Pry Bars
§ Bolt Cutters
§ Hammers
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Locking pliers are commonly
called Vise Grips. Vise Grips
is a Trade Name for the type
of tool.
Locking pliers incorporate
opposed jaws which grasp and
can be locked onto an object.
Class Characteristics of this
tool include:
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Needle nose locking pliers
work in the same fashion
as standard locking pliers,
however the jaws are
longer.
The measurable class
characteristics are the
same; jaw length, jaw
width, teeth spacing, jaw
lip length, and number of
teeth.
1
© Precision Forensic Testing
Slip Joint Pliers
n
n
Slip Joint Pliers are
commonly called
adjustable pliers because
they can be opened to
two different widths
The class characteristics
of slip joint pliers include:
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© Precision Forensic Testing
2
Jaw width
Jaw length
Teeth spacing
Jaw lip length
Number of teeth
© Precision Forensic Testing
Needle Nose Locking Pliers
3
Jaw width
Jaw length
Jaw lip length
Teeth spacing
Number of teeth
© Precision Forensic Testing
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Tongue and Groove Pliers
n
n
Tongue and Groove Pliers
n
Tongue and groove pliers are
commonly called Channel
Locks . Channel Lock is a brand
name of a company that makes
them.
The class characteristics of
tongue and groove joint pliers
include:
n  Jaw width
n  Jaw length
n  Jaw lip length (and teeth
size/spacing)
n  Teeth spacing
n  Number of teeth
n
These two tongue and groove
pliers appear to be the same
when given a quick look.
However, closer examination of
the jaws show the differences in
class characteristics.
These two tools would leave
different marks on any surface
they came in contact with.
© Precision Forensic Testing
© Precision Forensic Testing
Diagonal Cutters
Lineman's Pliers
n
n
Lineman's pliers have two
different working surfaces
which can come in contact
with wires.
n  The front section of the
jaws have serrated teeth
for gripping.
n  The rear section of the
jaws have blades for
cutting
n
Diagonal cutting pliers are
designed for cutting metal,
generally wires. They achieve
this by pinching the metal
between the cutting edges
The class characteristics of
wires cut by diagonal cutters
are a roof top shaping of the
cut surface.
Discuss the class characteristics
of Lineman s pliers.
© Precision Forensic Testing
© Precision Forensic Testing
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Pipe Wrenches
Wire Cutters/Strippers
n
n
Wire cutters/strippers are a
multifunction tool. They can be used
to strip insulation from wire when
only closed partially around the wire.
When closed completely, they can be
used to cut wire. This is achieved by
the sharpened opposing blades.
Class characteristics of wires cut by
these types of wire strippers have flat
surfaces.
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Pipe wrenches are also
called monkey
wrenches . They work
by grasping round objects
between the jaws.
The jaws are slightly
tapered inward and
tighten on the work piece
as the wrench is rotated.
© Precision Forensic Testing
Circular Cutting Tools
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© Precision Forensic Testing
Circular Cutting Tools
Circular cutting tools use a
rotating edge to remove
material. The most common
type of circular cutting tool is a
drill.
The drill bit (also called the
Morse drill after the inventor)
uses the edge of the bit to cut
the material. The waste
material, called swarf, is
drawn away from the hole by
the flutes in the drill bit.
The class characteristic of the
drill bit is the diameter.
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© Precision Forensic Testing
Drill bit manufacturers may
use different designs to
improve the cutting ability of
the drill bit.
This manufacturing design will
give different class
characteristics than traditional
drill bits.
© Precision Forensic Testing
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Chisels
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Screwdrivers
Chisels are bladed tools
designed to compress material
when struck. The bevel of
the chisel is the angled area
from the tip to the blade face.
Chisels have the following
measurable class
characteristics:
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Blade width
Blade thickness
Bevel thickness
Screwdrivers are
designed to impart torque
on a screw.
Screwdrivers may be
used as pry tools by
criminals.
Class characteristics of
screwdrivers include:
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Blade width
Blade thickness
Surface texture
© Precision Forensic Testing
© Precision Forensic Testing
Screwdriver – Class Characteristics
Screwdrivers
come in a variety
of shapes and
sizes. These are
measurable
features which
can be used in an
investigation to
include a tool for
further analysis
or exclude it from
having made a
mark.
Among these
characteristics is
the surface of the
blade. Notice the
various surface
textures.
Prybars
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© Precision Forensic Testing
Prybars are used to gain
leverage between two
objects. There are slots
in each end of a prybar to
ensure a solid grasp on a
smaller item such as a
nail.
© Precision Forensic Testing
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Prybars
n
Bolt Cutters
As with any other tool,
prybars come in a variety
of sizes. These
differences in class
characteristics include:
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Blade width
Blade thickness
Space between the blade
tips
Bolt cutters are designed
to cut steel bolts or rods.
They use a compound
pivoting action to provide
the maximum amount of
force on the jaws
© Precision Forensic Testing
© Precision Forensic Testing
Hammers
Hammers
n
n
n
Claw hammers get their
name from the split rear
area of the hammer used
to pull nails.
These are the most
common hammers
available and come in a
variety of shapes and
sizes.
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© Precision Forensic Testing
In addition to the face of the
hammer, the rear claws can be
used as a tool.
List the class characteristics of
a hammer.
© Precision Forensic Testing
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Tools - Compression
Tools – Classification
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Tools can also be classified according to type of
action it imparts on the work piece. The action
affects the marks left on the work piece.
Examples of different types of actions include:
n  Compression
n  Flat Action
n  Gripping
n  Shearing
n  Slicing
n
Compression tools are
designed to compress by
pressure or impact.
These tools include
hammers, chisels, and die
stamps.
© Precision Forensic Testing
© Precision Forensic Testing
Tools – Flat Action
n
Tools – Gripping Action
Flat action tools work in
parallel to the working
surface. These types of
tools include screwdrivers,
pry bars and tire irons.
n
© Precision Forensic Testing
These tools use
opposing jaws to
squeeze or hold an
object. Tools in this
category include vise
grips, tongue and
groove pliers, and
pipe wrenches.
They are also called
serrated jaw
gripping tools.
© Precision Forensic Testing
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Tools – Shearing Action
Tools - Pinching Action
These tools use opposed jaws
which are designed to cut
using a pinching action.
Examples of these types of
tools include bolt cutters and
diagonal cutters.
Shearing tools use two blades
on adjacent planes that pass by
each other and are designed to
cut. These types of tools
include scissors, tin snips, wire
cutters, and pruning shears.
© Precision Forensic Testing
© Precision Forensic Testing
Individual Characteristics
Tools – Slicing Action
n
n
Slicing tools cut materials
by moving a sharp blade
along the direction in
which it is traveling.
These tools include knives
and razors.
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Within the class characteristics
are the individual
characteristics. These are
microscopic imperfections on
the edge of the cutting
surface.
They are caused by:
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© Precision Forensic Testing
The manufacturing process
Use
Abuse
Rust
© Precision Forensic Testing
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Tools – Manufacturing
Individual Characteristics
n
n
Because individual characteristics
are unique on the surface of the
tool, they are essentially
fingerprints.
These unique marks will be
transferred on any object they
come in contact with.
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By understanding how tools are made, we can understand how the
class and individual characteristics are made.
Tools are typically made using a combination of machining methods.
The initial shape of the tool may be stamped from a solid piece of
metal.
Another way to make the basic shape of tools is by forging.
Forging involves shaping the metal into the desired shape under
high pressure. This is typically done by a hammering action.
Tools can have the final shape and cutting edge made by milling or
grinding.
Screwdriver blade tip at 20X magnification
Lineman s pliers blade at 20X
magnification
© Precision Forensic Testing
© Precision Forensic Testing
Stamping
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Grinding
Some blades of tools are
made from steel barstock.
The barstock is fed into a
hydraulic press that acts as
a cookie cutter that
stamps out the basic shape
of the tool blade.
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© Precision Forensic Testing
Grinding is a method used to
put an edge on a blade.
A grinding wheel is composed
of small stone fragments
embedded in a matrix. The
surface of the grinding wheel
is always changing as it comes
in contact with metal. This
causes the marks it makes to
be individual.
© Precision Forensic Testing
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Grinding
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Milling
Surfaces that are ground
typically have parallel marks
The individual characteristics
of a ground surface can be
seen below.
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Milling machines remove
metal using a rotating
carbide cutter.
Unlike a drill, mills can cut
using the side or the end of
the bit.
© Precision Forensic Testing
Milling
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The raw stamping of the blade
is placed in a milling machine
to cut the contour of the
cutting blade into the
stamping.
This will commonly require
two passes. The first pass
cuts the basic shape of the
blade. The next pass cuts the
secondary cutting angle.
© Precision Forensic Testing
© Precision Forensic Testing
Milling
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n
The milling process leaves
marks in the direction of the
travel of the mill. In this
example, the mill cut parallel
to the edge.
The individual characteristics
can be seen in the picture
below.
© Precision Forensic Testing
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Toolmarks - Impressed
Toolmarks
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n
Two types of toolmarks that can be made when
a tool comes in contact with an object. They are
impressed and striated.
These marks are reproducible and can be used
for comparison and identification of a toolmark
to a particular tool.
* Association of Firearm and Tool Mark Examiners Glossary 4th Edition
© Precision Forensic Testing
© Precision Forensic Testing
Toolmarks - Impressed
Toolmarks - Impressed
n
n
Impressed Toolmark - The
mark produced when a tool
is placed against an object
and enough pressure is
applied to the tool so that it
leaves an impression in the
object. The class
characteristics (shape) can
suggest the type of tool used
to produce the mark. The
individual characteristics can
be used to identify the tool
with the mark. Also called
Compression Mark.*
Impressed marks can be left by a variety of tools. The most
common are bolt cutters, pry bars, chisels, and hammers.
© Precision Forensic Testing
n
Impressed marks are mirror images
of the tool that left the impression.
Any imperfections in the tools
surface will be imparted to the work
piece and can be used for
comparison and identification.
© Precision Forensic Testing
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Toolmark - Comparisons
Toolmarks - Impressed
n
Bolt cutters are another
tool that leave impressed
marks as they squeeze
the material in the cutting
process.
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Compressed marks
from bolt cutters
can be used for
comparisons.
The individual
characteristics of
the bolt cutter
blades reproduce on
the surfaces they
come in contact
with.
© Precision Forensic Testing
© Precision Forensic Testing
Tools - Comparisons
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© Precision Forensic Testing
Toolmarks made by compression tools yield mirror images of the tool.
Any defects on the surface of the tool will be transposed onto the
surface of the item it comes in contact with.
The overall size and shape of the imprint is measurable and a class
characteristic of the tool.
Stamp
Stamped Impression
© Precision Forensic Testing
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Toolmarks - Striated
n
Toolmarks - Striated
n
Marks produced when a
tool is placed against
another object and with
pressure applied, the tool is
moved across the object
producing a striated mark.
Friction marks, abrasion
marks and scratch marks
are terms commonly used
when referring to striated
marks.*
* Association of Firearm and Tool Mark Examiners Glossary 4th Edition
© Precision Forensic Testing
© Precision Forensic Testing
Toolmarks - Comparisons
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The most common tool that
leaves striated marks
encountered in crime
laboratories is a screwdriver.
Criminals typically use
screwdrivers to try to pry open
cash drawers, windows, doors,
and car locks.
Toolmark - Comparisons
The striated toolmarks created
by flat action tools are
reproducible and can be used
for comparison between the
mark and test marks made by
that tool.
When making test marks a
softer metal is used, typically
lead. Lead will not damage
the blade during the course of
making test marks, yet is hard
enough accept the marks.
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© Precision Forensic Testing
The first step in performing a
comparison of striated
toolmarks is to establish the
correspondence of class
characteristics.
This will typically be blade width
or spacing of the blades if a tool
such as a pry bar is used.
© Precision Forensic Testing
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Toolmarks - Comparisons
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Toolmarks - Striated
After correspondence of the class characteristics has been
established, the individual characteristics can be evaluated.
We can use these individual characteristics to conclude that the
same tool made both marks.
n
Another tool that leaves
striated marks when
contacting a surface is a drill
bit. Drill bits cut as they
rotate, therefore the striated
marks are circular. These
striated marks are caused by
imperfections on the cutting
edge of the blade.
© Precision Forensic Testing
© Precision Forensic Testing
Toolmarks - Comparisons
Toolmarks - Striated
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As with striated toolmarks from
bladed tools, striated marks
from drill bits can be compared
to each other.
This is an example of an
evidence mark on the left and
a test mark made by the
suspect drill on the right.
n
© Precision Forensic Testing
There are times when the
toolmark can not be
removed from the location
for submission to a crime
laboratory. When this
occurs the toolmark must
be cast.
Casting makes a negative
impression of the toolmark
and is typically done with
Mikrosil.
© Precision Forensic Testing
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Toolmarks - Comparisons
Toolmarks - Comparisons
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n
Mikrosil is a two part
system that must be
mixed prior to using.
After it has been
completely mixed, the
Mikrosil can be applied
to the area of the
toolmark.
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The casting is documented
while in place as part of the
crime scene photos and
documentation process.
After it has hardened, it can
be peeled from the surface.
The casting will be submitted
to the crime laboratory for
comparison to the tool.
© Precision Forensic Testing
© Precision Forensic Testing
Toolmarks - Comparisons
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Case Study
The casting of the
toolmark is a mirror
image, therefore a
casting of the test marks
must be made for
comparison.
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© Precision Forensic Testing
Police are called to a
bar at approximately
7:00 a.m.
One male victim located
in the bathroom
One male victim located
in a back room.
Both had been beaten
to death by a blunt
object.
© Precision Forensic Testing
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Case Study
Case Study
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A possible suspect was identified as having been seen
leaving the back door of the bar after it had closed.
The witness was unable to positively identify the suspect
due to the lighting conditions and distance.
The scene inside the bar was not conducive for
fingerprint processing due to the volume of patrons who
had been in the bar.
No DNA from a suspect was located to assist in the
investigation.
There was very little forensic evidence due to the type of
establishment and number of people who had access to
the location prior to the crime.
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n
Crime Scene Personnel,
Detectives, and Lab Analysts
met to discuss the case and
what evidence could be obtained
to establish a suspect.
Damage to a cigarette machine
was noted and it was discovered
that the suspect had broken into
the machine to get money.
© Precision Forensic Testing
© Precision Forensic Testing
Case Study
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Case Study
Toolmarks on the cigarette
machine were cast for
comparison if a tool were
to be located.
Analysis of the toolmarks
established that the type of
tool used was a pry bar.
This information was given
to the case detective
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© Precision Forensic Testing
Based on the information
that the probable tool
was a pry bar, detectives
searched the vehicle of
the suspect.
© Precision Forensic Testing
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Case Study
Case Study
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n
A search of the suspects
trunk revealed a pry bar.
Detectives secured the pry
bar and submitted it to the
crime lab for comparison to
the toolmarks from the
cigarette machine.
n
n
© Precision Forensic Testing
Comparison of the
toolmark from the
cigarette machine to test
marks made by the
suspect s pry bar yielded
an identification.
The toolmark
identification placed the
suspect at the crime
scene and led to a
conviction in a double
homicide.
© Precision Forensic Testing
17