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Science Behind Tool Marks - Forensic Science Analysis and Lab | FRSC 4253, Study notes of Forensics

University of Central Oklahoma (UCO)Forensics

science behind toolmarks Material Type: Notes; Class: Forensic Sci Analysis & Lab; Subject: Forensic Science; University: University of Central Oklahoma; Term: Spring 2011;

Typology: Study notes

2010/2011

Uploaded on 01/21/2011

acusack5559
acusack5559 🇺🇸

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The Science behind Toolmarks
Toolmark Examinations
oPurpose
The purpose of this module is to introduce you to the AFTE Theory of
identification as it relates to Firearm and Toolmark Examination
oObjectives
At the conclusion of the module you will know the following:
The association of firearm and toolmark examiners theory of
identification
What toolmark examination is in regards to:
oFirearms
oToolmarks
How to establish criteria for identification
oHistory
Toolmark identification as a forensic discipline has been around for over
40 years
However the earliest known toolmark identification was in 1835 in
London, England
Slave accused of killing his owner
Muzzle loading guns used paper
oTorn paper was found in the floor (fracture matching)
oAFTE Theory of Identification
Enables opinions of common origin to be made where two surface
contours are in “sufficient agreement” with one another
What is meant by the term “sufficient agreement?”
Refers to the possibility that another tool or tools could have made
the same mark or marks is so remote as to be considered a
practical impossibility.
oDefining Science or Art
The field is built upon scientific methods
What is science?
oA collaboration of investigations
oInvestigating phenomena and acquiring new knowledge, as
well as for correcting and integrating previous knowledge.
It is based on gathering observable, empirical, measurable
evidence, subject to specific principles of reasoning
What is art?
oBy definition it is a process of deliberately arranging
symbolic elements in a way that influences and affects the
senses, emotions, and/or intellect
oThroughout history the term art was referred to as any skill
or mastery
oThe science of firearm and toolmark identification
Toolmark identification as a science
Toolmark identification is the discipline
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The Science behind Toolmarks  Toolmark Examinations o Purpose  The purpose of this module is to introduce you to the AFTE Theory of identification as it relates to Firearm and Toolmark Examination o Objectives  At the conclusion of the module you will know the following:  The association of firearm and toolmark examiners theory of identification  What toolmark examination is in regards to: o Firearms o Toolmarks  How to establish criteria for identification o History  Toolmark identification as a forensic discipline has been around for over 40 years  However the earliest known toolmark identification was in 1835 in London, England  Slave accused of killing his ownerMuzzle loading guns used paper o Torn paper was found in the floor (fracture matching) o AFTE Theory of Identification  Enables opinions of common origin to be made where two surface contours are in “sufficient agreement” with one another  What is meant by the term “sufficient agreement?”  Refers to the possibility that another tool or tools could have made the same mark or marks is so remote as to be considered a practical impossibility. o Defining Science or Art  The field is built upon scientific methods  What is science? o A collaboration of investigations o Investigating phenomena and acquiring new knowledge, as well as for correcting and integrating previous knowledge. It is based on gathering observable, empirical, measurable evidence, subject to specific principles of reasoning  What is art? o By definition it is a process of deliberately arranging symbolic elements in a way that influences and affects the senses, emotions, and/or intellect o Throughout history the term art was referred to as any skill or mastery o The science of firearm and toolmark identification  Toolmark identification as a science  Toolmark identification is the discipline

 The ability to determine if a specific tool was used to create a specific mark or marks  Firearms identification as a science  Firearm identification is part of the process of toolmark identification, not a discipline  The ability to determine if a specific ammunition component was fired from, by, or in a particular firearm o depends on what you haveexample, loading the magazine, cycle the gun, but not firing the gunbullet can be fired by a guncartridge case can be fired by a gun o What is a tool?  Mechanical advantage  Anything used to gain mechanical advantage  Can firearms be used to gain mechanical advantage?  Yes  Guns are a tool o They used to be used for a purposeSurvivalHunting  Types of toolmarks o Background  Toolmarks occur when two objects come into contact with each other  Describing a toolmark:  Striated (striations)  Impressed (indentions) o Striated toolmarks  Striated toolmarks have a series of ridges or linear marks  Rubber being cut by knifeScrewdriver dragged across a surface  Striated marking on a cartridge case fired in a firearm o Elliptical firing pin impressionPolygonal bulletsStriated or shearing marks on both left and right hand sides of firing pin impressionDragging causes oblong impression  Striated markings on a copper elbow obtained from a pair of pliers o Striated tools  Tools considered to slide or scrape across a surface and follow the motion of the tool.  Examples consist of:  Screw driver  Pliers  Knifes  Extractor marks on a cartridge case

o Individual characteristics  Inconsistencies  Random imperfections created on tool surfaces during manufacturing and during the lifespan of the tool  While these imperfections are incidental to the manufacturing process they can also be due to use, abuse, corrosion, and damage of the manufacturing tools surface.  If you don’t take care of an item, it is going to wear on itself o E.g. rust  All individual characteristics are unique to a particular tool and distinguish it from all other tools  You are not identifying it to a person, you are identifying to an objectNot ever exact  “every tool has a fingerprint”  Examples of individual characteristics:  Unique differences in chatter marks on a tool or surface (imperfection or wear)  Circular versus striated impressions on breech face area of a cartridge case of the same caliber  Individual characteristics are the differences within each tool that set it apart from the other tools within a class of tools  For instance, the individual differences seen between impressions made by those same screwdrivers all consecutively manufactured  Or two 9mm cartridge cases fired by different guns one with circular impressions, the other with striated or linear markings o Establishing Criteria  You have to have a known and an unknown  The many differences in production techniques offer various forms of individuality among classes of tools  In production, the bits that are used to make the tools go through increasing amounts of wear  Ultimately creating more individuality amongst the tools in the class  The same happens in firearms o http://science.discovery.com/videos/how-its-made-season- 6/ o Swiss army knife assemblyIndividual characteristics are created when they sand down the blades from their rough “stamped“ edges o Methodology  In order to conduct a sound examination you must have a known and unknown  If you are just given a toolmark, all you can give them is a list of possibilities

 The known being the source or toolmark present  The unknown being the tool or group of tools used to create the toolmark obtained  The class characteristic must fit the design pattern or be closely similar to the toolmark present o Similar class characteristics  Similar base diameters  Similar land and groove widths o Different class characteristics  4R  6L o Range of Conclusions  Identification  Agreement of all discernable class characteristics and all discernable individual characteristics  Elimination  Significant disagreement of class and/or individual characteristicsNothing matches at all, not even close  Inconclusive  Some agreement of individual characteristicsSome agreement of class characteristicsBut not enough for an identification o It feels good, but not good enough o If someone is verifying and can’t get the same conclusion o If you don’t feel good making the call, the benefit of the doubt always goes to the defendantDon’t push your look, it will ruin your credibility  Unsuitable for examination purposes  Unsuitable for microscopic examination o Key factors in the examination of toolmarks  Examining and evaluating is of the most importance  A submitted toolmark and no tool does not equal no examination  Random possibilities of likely tools is all that can be found  Extensive training and experience in the comparison of toolmarks is essential in providing quality investigative leads  Set yourself apart from the average person o Know everything about that tool regardless of your conclusion on the case  Microscopic analysis of toolmarks o Comparison Macroscope  Most useful tool within the examination of fired ammunition components and toolmark examination  Defining an instrument  Macroscope o 100x magnification and lower  Microscope

o Take measurements on the scope