Toolmarks

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Toolmarks

  1. 1. ToolmarksA toolmark is defined as the impression left by the contact of a tool (or a similar object) onto asurface. When the tool or object contacts the surface with sufficient force to create anindentation, the pattern of the tool is permanently reproduced onto that surface. Toolmarksexamination is an important discipline of criminalistics. Its goal is to establish a link between atoolmark and the tool that created it. Such links are crucial in forensic sciences, as tools are oftenused in criminal activities, particularly in burglaries, and can help to identify a criminal. Forexample, when a burglar uses a pry bar to force entry into a house, the marks left by the tool onthe door frame are direct evidence of the presence of that tool for that particular use at the crimescene. If the tool is found with, or near, a suspect, it permits the establishment of a link betweenthe suspect and the crime scene. Thus, the recognition and collection of toolmarks at the crimescene and their examination at the laboratory are paramount.Toolmarks bear two kinds of characteristics: class and individual. The class characteristics of atoolmark include the type of impression, its general shape, and its general dimensions. Classcharacteristics typically allow the examiner to determine what type of tool created the impressionand how the mark was created. Conversely, they do not permit for the identification of the exacttool that created the impression. This means that if only class characteristics are available on atoolmark, it will not be possible to distinguish which tool, among a series of similar tools, madethe impression. Individual characteristics, also called accidental characteristics, are the striationsand small particularities exhibited by the tool that are individual to one unique tool. They consistof small, commonly microscopic, indentations, ridges, and irregularities present on the tool itself.For example, the tip of a screwdriver is never perfectly flat, but shows small ridges along itsedge. These are created by the history of the tool such as its use and misuse, its cleaning, and itsmaintenance. These characteristics are the only ones that permit a formal identification. If suchcharacteristics are present in the toolmark, it is possible to identify the actual individual tool thatcreated the impression, even among a series of identical tools.There are two main types of toolmarks that can be distinguished: slipped and moldedimpressions. The slipped impression occurs as the tool drags or slides across the surface. Theresulting toolmark is a series of striations running parallel to each other following the directionof the drag. For example, such impressions are created by slipping a key across the door of avehicle, by cutting with a knife (not used in a sawing motion) through a given material, or bycutting an electrical wire using a pair of linemans pliers. The molded impressions are the resultof the contact of a tool onto a surface with no lateral motion (no drag nor slip). The resultingtoolmarks are a three-dimensional mold of the part of the tool that contacted the surface.Examples of such impressions are the leverage of a door from its frame with a pry bar, or theserial number stamped onto a fire-arms barrel. Some toolmarks are made of a combination ofmolded and slipped impressions.
  2. 2. Toolmark examination is a term that includes a wide variety of impressions that are notnecessarily directly related to tools but that are created via the same fashion and are, therefore,examined with the same techniques. A clear example is the impression left by a firearms barrelonto a bullet or by the firearm onto the cartridge. These are a specialized category of toolmarks.Other examples include the impressions left by human teeth or even the impressions left byshoes or tires. Very often, the toolmark examiner is the person responsible for examining andrendering expert opinions on such impressions identifications.The examination of toolmarks is conducted in different phases. First, the toolmark is observed,measured, and described. Second, a photograph perpendicular to the toolmark, is taken. Thisprovides a permanent record of the class and some individual characteristics of the toolmark.Then, if the support onto which the toolmark is located cannot be collected as evidence, a cast ofthe toolmark is made. This cast is usually made with polymeric dental paste. When a tool isdiscovered and its class characteristics match the ones exhibited by the toolmark, the comparisonprocess is started. Usually, the tool is observed and photographed. Then, comparison tool-marksare made with the tool on a soft material so that extra marks are not created on the tool. Acomparison microscope is used to perform the comparison process. The incriminated toolmark isplaced on the left side of the microscope and the comparison mark on the right side. If a matchexists between the individual characteristics, the common origin between the incriminatedtoolmark and the tool is established.Importance of Tool marks 1. Frequency A criminal often uses some tools in commission of a crime. If he is prying open a window, he uses a crow bar or a screw driver; if he is opening a lock, he uses a ghost key, a master ker or a cutter; if he is felling a tree, he uses axe or a saw, if he has entered a house after diggiging a hole in the wall he uses some digging implements; like spade or shovel. If he has stolen copper wire or cable he must have used some wire cutter. Thus, thus the occurrence of tool marks is almost universal in all type of crimes. 2. Permanency A tool made of a hard metal. The surface on which it makes marks is ordinarily, made of softer material. The tool is not damaged in the process to any appreciable extent. If the tool is not extensively used or misused and if the same is properly maintained, the marks are reproducible almost indefinitely. Thus a criminal can be linked even after a long interval through the tool (recovered from the criminal) and the tool marks collected from the scene.
  3. 3. 3. Individuality The tool marks like figure print foot and footwear marks and marks on bullet and cartridges provides a definite link between the crime and the criminal. For example, a piece of wire is stolen (by cutting). The cut end left is send to the laboratory along with the tool recovered from the suspect, the wire is found to have been cut from the tool recovered from the suspect, the theft is pinned to him. This is because no two tools even of the same make and batch, made one after the other will have identical surface leave identical marks on the surface cut, graced or scratched by them. 4. Linkage A culprit usually uses the same set of tools in the same type of crime. If the tools marks from various crimes are compared inter se and found identical, the crime are linked. 5. Reconstruction Carefully study of the nature, position, direction and number of tool marks help in reconstruction of crime and thus it is possible to verify the prosecution or defence version of the crime.Evidentiary value of ToolmarksToolmark impressions are usually microscopic and are the result of the imperfections found onthe cutting surface of a tool. These marks are the "signature" or identifying characteristics of aspecific tool.Laboratory examinations and comparisons of toolmarks from a “suspect tool“ with toolmarksrecovered from a crime scene can often prove conclusive evidence to link a suspect to a specificcrime and wrap up the criminal investigation.Creating a Link Between the Toolmark and the ToolIn a criminal investigation, the goal is to establish a link between a toolmark and the tool thatcreated it at the crime scene. Such links are crucial in forensic sciences, as tools are often used incriminal activities, particularly in burglaries, and can help to identify a criminal. For example,when someone uses a screw driver to force a window open, the marks left by the tool on thewindow frame are direct evidence of the presence of that tool for that particular use at the crimescene. (Then the tool needs to be matched to its owner)
  4. 4. Evidence Submitted in Toolmark Cases May Include Tools like: bolt cutters screwdrivers and chisels scissors knives and box cutters pliers and wrenches crowbars tire irons saws, knivesPlaces and Surfaces where Toolmarks Might be Observed in Criminal Investigations: wire, chains door and window frames sections of sheet metal safety-deposit boxes, safes human bone or cartilage padlocks, doorknobs bolts and locks and a variety of other materials.Toolmarks can be Scratches or ImpressionsToolmarks can be scratches and/or impressions that are left on a surface that is softer than theobject or tool that caused the marks. At a crime scene, the unique and individual imperfectionson the tool surfaces - that are transferred to the softer surface of the damaged object - can be usedto make a positive identification of the tool that may have been used to cause the toolmarkstriations or impressions.Minute Scratches - Toolmark StriationsMinute scratches (striations) produced by tests made in the crime laboratory by the questionedtool, will be compared to the striations noted on the evidence toolmark areas.The forensic scientist (toolmark examiner) using a comparison microscope will conductcomparison examinations to determine whether or not a particular tool may or may not havecaused the markings on the evidence from the crime scene.
  5. 5. Impressed Marks - Crowbars, Car Bumpers, ScrewdriversImpressed marks are also considered to be toolmarks. For example, the tip of a screwdriver orchisel that is used to indent a metal surface but does not penetrate the object will leave animpression that can be identified to that tool.Other tools like crowbars, hammers and even larger objects like car bumpers or bull bars mayleave identifying marks and impressions that, when compared in the crime laboratory, willidentify or eliminate the tool or object from the crime scene as being the one that made theimpression.

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