Toolmarks
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Toolmarks are impressions left by tools that come into contact with surfaces. They contain both class characteristics about the type of tool and individual characteristics unique to a specific tool. Toolmark examination aims to link toolmarks at a crime scene to the actual tool used. This can help identify criminals, as tools are often involved in crimes like burglaries. Minute striations and impressions on tools are transferred to softer surfaces, and toolmark examiners use microscopes to compare crime scene marks to test marks made by suspect tools to determine matches. Toolmarks provide important forensic evidence that can link crimes and criminals.
Toolmarks
- 1. Toolmarks A toolmark is defined as the impression left by the contact of a tool (or a similar object) onto a surface. When the tool or object contacts the surface with sufficient force to create an indentation, the pattern of the tool is permanently reproduced onto that surface. Toolmarks examination is an important discipline of criminalistics. Its goal is to establish a link between a toolmark and the tool that created it. Such links are crucial in forensic sciences, as tools are often used in criminal activities, particularly in burglaries, and can help to identify a criminal. For example, when a burglar uses a pry bar to force entry into a house, the marks left by the tool on the door frame are direct evidence of the presence of that tool for that particular use at the crime scene. If the tool is found with, or near, a suspect, it permits the establishment of a link between the suspect and the crime scene. Thus, the recognition and collection of toolmarks at the crime scene and their examination at the laboratory are paramount. Toolmarks bear two kinds of characteristics: class and individual. The class characteristics of a toolmark include the type of impression, its general shape, and its general dimensions. Class characteristics typically allow the examiner to determine what type of tool created the impression and how the mark was created. Conversely, they do not permit for the identification of the exact tool that created the impression. This means that if only class characteristics are available on a toolmark, it will not be possible to distinguish which tool, among a series of similar tools, made the impression. Individual characteristics, also called accidental characteristics, are the striations and small particularities exhibited by the tool that are individual to one unique tool. They consist of 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 its edge. These are created by the history of the tool such as its use and misuse, its cleaning, and its maintenance. These characteristics are the only ones that permit a formal identification. If such characteristics are present in the toolmark, it is possible to identify the actual individual tool that created the impression, even among a series of identical tools. There are two main types of toolmarks that can be distinguished: slipped and molded impressions. The slipped impression occurs as the tool drags or slides across the surface. The resulting toolmark is a series of striations running parallel to each other following the direction of the drag. For example, such impressions are created by slipping a key across the door of a vehicle, by cutting with a knife (not used in a sawing motion) through a given material, or by cutting an electrical wire using a pair of lineman's pliers. The molded impressions are the result of the contact of a tool onto a surface with no lateral motion (no drag nor slip). The resulting toolmarks 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 the serial number stamped onto a fire-arm's barrel. Some toolmarks are made of a combination of molded and slipped impressions.
- 2. Toolmark examination is a term that includes a wide variety of impressions that are not necessarily 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 firearm's barrel onto 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 by shoes or tires. Very often, the toolmark examiner is the person responsible for examining and rendering expert opinions on such impression's 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. This provides 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 of the toolmark is made. This cast is usually made with polymeric dental paste. When a tool is discovered and its class characteristics match the ones exhibited by the toolmark, the comparison process is started. Usually, the tool is observed and photographed. Then, comparison tool-marks are made with the tool on a soft material so that extra marks are not created on the tool. A comparison microscope is used to perform the comparison process. The incriminated toolmark is placed on the left side of the microscope and the comparison mark on the right side. If a match exists between the individual characteristics, the common origin between the incriminated toolmark 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. 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 Toolmarks Toolmark impressions are usually microscopic and are the result of the imperfections found on the cutting surface of a tool. These marks are the "signature" or identifying characteristics of a specific tool. Laboratory examinations and comparisons of toolmarks from a “suspect tool“ with toolmarks recovered from a crime scene can often prove conclusive evidence to link a suspect to a specific crime and wrap up the criminal investigation. Creating a Link Between the Toolmark and the Tool In a criminal investigation, the goal is to establish a link between a toolmark and the tool that created it at the crime scene. Such links are crucial in forensic sciences, as tools are often used in criminal 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 the window frame are direct evidence of the presence of that tool for that particular use at the crime scene. (Then the tool needs to be matched to its owner)
- 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, knives Places 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 Impressions Toolmarks can be scratches and/or impressions that are left on a surface that is softer than the object or tool that caused the marks. At a crime scene, the unique and individual imperfections on the tool surfaces - that are transferred to the softer surface of the damaged object - can be used to make a positive identification of the tool that may have been used to cause the toolmark striations or impressions. Minute Scratches - Toolmark Striations Minute scratches (striations) produced by tests made in the crime laboratory by the questioned tool, will be compared to the striations noted on the evidence toolmark areas. The forensic scientist (toolmark examiner) using a comparison microscope will conduct comparison examinations to determine whether or not a particular tool may or may not have caused the markings on the evidence from the crime scene.
- 5. Impressed Marks - Crowbars, Car Bumpers, Screwdrivers Impressed marks are also considered to be toolmarks. For example, the tip of a screwdriver or chisel that is used to indent a metal surface but does not penetrate the object will leave an impression that can be identified to that tool. Other tools like crowbars, hammers and even larger objects like car bumpers or bull bars may leave identifying marks and impressions that, when compared in the crime laboratory, will identify or eliminate the tool or object from the crime scene as being the one that made the impression.