Forensic Sci Analysis & Lab
Forensic Sci Analysis & Lab FRSC 4253
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This 7 page Class Notes was uploaded by Alessia Huels on Thursday October 22, 2015. The Class Notes belongs to FRSC 4253 at University of Central Oklahoma taught by Staff in Fall. Since its upload, it has received 29 views. For similar materials see /class/227708/frsc-4253-university-of-central-oklahoma in Forensic Science at University of Central Oklahoma.
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Date Created: 10/22/15
The Science behind Toolmarks o Toolmark Examinations 0 Purpose I The purpose of this module is to introduce you to the AFTE Theory of identi cation as it relates to Firearm and Toolmark Examination 0 Objectives I At the conclusion of the module you will know the following o The association of rearm and toolmark examiners theory of identi cation What toolmark examination is in regards to o Firearms o Toolmarks How to establish criteria for identi cation 0 History I Toolmark identi cation as a forensic discipline has been around for over 40 years I However the earliest known toolmark identi cation was in 1835 in London England 0 Slave accused of killing his owner 0 Muzzle loading guns used paper 0 Torn paper was found in the floor fracture matching 0 AFTE Theory of Identi cation I Enables opinions of common origin to be made where two surface contours are in suf cient agreement with one another I What is meant by the term suf cient agreement 0 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 De ning Science or Art I The eld is built upon scienti c methods 0 What is science 0 A collaboration of investigations 0 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 speci c principles of reasoning o What is art 0 By de nition it is a process of deliberately arranging symbolic elements in a way that in uences and affects the senses emotions andor intellect 0 Throughout history the term art was referred to as any skill or mastery o The science of rearm and toolmark identi cation I Toolmark identi cation as a science 0 Toolmark identification is the discipline 0 o The ability to determine if a speci c tool was used to create a speci c mark or marks I Firearms identi cation as a science 0 Firearm identi cation is part of the process of toolmark identification not a discipline 0 The ability to determine if a speci c ammunition component was red from by or in a particular rearm 0 depends on what you have I example loading the magazine cycle the gun but not firing the gun I bullet can befired by a gun I cartridge case can be fired by a gun o What is atool I Mechanical advantage 0 Anything used to gain mechanical advantage I Can rearms be used to gain mechanical advantage 0 Yes 0 Guns are a tool 0 They used to be used for a purpose I Survival I Hunting 0 Types of toolmarks 0 Background I Toolmarks occur when two objects come into contact with each other I Describing a toolmark o Striated striations o Impressed indentions o Striated toolmarks I Striated toolmarks have a series of ridges or linear marks 0 Rubber being cut by knife 0 Screwdriver dragged across a surface 0 Striated marking on a cartridge case red in a rearm o Ellipticalfiring pin impression I Polygonal bullets I Striated or shearing marks on both left and right hand sides of firing pin impression I Dragging causes oblong impression o Striated markings on a copper elbow obtained from a pair of pliers o Striated tools I Tools considered to slide or scrape across a surface and follow the motion of the tool I Examples consist of 0 Screw driver 0 Pliers o Knifes o Extractor marks on a cartridge case 0 Claw on inside ofgun I Holds on to base of cartridge case at extractor grooves I Causes it to be twisted out o Impressed tools I Tools that used forcefully against another surface and leave an impression or imprint I Examples consist of o Hammers o If it can t create an impression on the object it will break the object o Chisels 0 Bolt cutters o Breech bolt in a firearm o Slams into the back of the cartridge case 0 Impressed toolmarks I Impressed toolmarks leave an imprint of the tool on the surface 0 Impressed markings on a cartridge case fired in a firearm 0 Flow bac I Rippling on cartridge case I Comes back at shooter I Bulges the primer area 0 Impressed markings on a lock obtained from a pair of bolt cutters o Striations inside the impression I It is possible to have both 0 Toolmark Classification 0 Toolmarks are classified by the marks they exhibit during the manufacturing process or throughout the lifespan of the tool 0 Class characteristics may be the same but individual characteristics will always be different I Class characteristics I Individual characteristics 0 Class characteristics I All class characteristics are determined prior to manufacturing and are measurable Features of a tool that are consistent with all other tools within that class Two same make and model screwdrivers would have the same class characteristics Examples of class characteristics 0 Size 0 Shape 0 Distance between discemable features ie teeth on a saw blade claws of a hammer etc 0 Width of lands and grooves 0 Overall length 0 Length of cartridge case 0 Individual characteristics 0 Establi 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 0 If you don t take care of an item it is going to wear on itself 0 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 object Not 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 0 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 shing 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 httn39 ciem e discovervcom 39J 6 0 Swiss army knife assembly I Individual characteristics are created when they sand down the blades from their rough stamped edges it madeseason 0 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 I The class characteristic must t the design pattern or be closely similar to the toolmark present 0 Similar class characteristics I Similar base diameters I Similar land and groove widths 0 Different class characteristics I I 6L 0 Range of Conclusions I Identi cation 0 Agreement of all discernable class characteristics and all discernable individual characteristics I Elimination 0 Signi cant disagreement of class andor individual characteristics 0 Nothing matches at all not even close I Inconclusive 0 Some agreement of individual characteristics 0 Some agreement of class characteristics 0 But not enough for an identification 0 It feels good but not good enough 0 If someone is veri ving and can t get the same conclusion If you don t feel good making the call the bene t of the doubt always goes to the defendant I Don t push your look it will ruin your credibility I Unsuitable for examination purposes 0 Unsuitable for microscopic examination 0 Key factors in the examination of toolmarks I Examining and evaluating is of the most importance I A submitted toolmark and no tool does not equal no examination 0 Random possibilities of likely tools is all that can be found I Extensive training and experience in the comparison of toolmarks is essential in providing quality investigative leads 0 Set yourself apart from the average person 0 Know everything about that tool regardless of your conclusion on the case 0 Microscopic analysis of toolmarks 0 Comparison Macroscope I Most useful tool within the examination of red ammunition components and toolmark examination I De ning an instrument 0 Macroscope O o 100x magni cation and lower 0 Microscope o 100x magni cation and higher I The unit is comprised of a two compound microscopes connected by an optical bridge 0 Look at two objects simultaneously through binocular lenses I Lighting advantagesdisadvantages 0 Fiber optics 0 Advantages I Illuminates well and can be adjusted o Disadvantages I Heat sensitive yellow light 0 Heats up very fast 0 Can place di users on them 0 Lowers intensity of light and broadens them out o Fluorescents 0 Advantages I Pure white light and is a consistent beam 0 Can see light beams constantly radiating o Keeps whole area illuminated o Disadvantages I Time consuming to adjust I Have to constantly move to adjust to right area depending on what stage you are on 0 Dealing with issues ofshadows oflight I Toolmark holders 0 Ball cup stage mount 0 Leeds vice 0 Has pliers in picture 0 Leeds document holder I Firearm examination holders 0 Leeds universal holder 0 Can swivel arm any direction 0 Leeds pin mounts 0 Has bullet inpicture 0 Leeds magnetic mounts 0 Has shotgun shell in picture I Advanced features 0 Binocular viewing 0 Image capturing components 0 Take a still 2D image and add measurements to it o Rotating nosepiece 0 Left right up and down Motorized height adjustment 0 Table of microscope 0 Digital reference marks 0 Take measurements on the scope
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