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Unit2_Toolmark impressions.pptx
- 2. TOOL MARKS IMPRESSIONS This Photo by Unknown Author is licensed under CC BY-SA Tool Toolmark
- 4. FORENSIC SIGNIFICANCE OF TOOL MARKS
- 6. TYPES OF TOOL MARKS Compression type marks/Indentation marks Striated marks/Abrasion marks Cutting marks Combination of compression and striated marks
- 7. Source: RG Nichols 2000 Source: RG Nichols 2000 Cutting marks
- 8. Source: RG Nichols 2000 Combination of compression and striated marks
- 9. FORENSIC EXAMINATION Tool mark examination from Crime Scene Toolmark Documentation (photography/tracing/lifting of toolmarks by casting) Examination of Foreign material Taking test impression Comparison of toolmark impression
- 10. TOOL SURFACE CHARACTERISTICS • Tools have unique characteristics resulting from manufacturing processes and from use over time. • Nicks, ridge marks, and blemishes may develop on the striking surface of the tool. • These unique characteristics from natural wear and tear can affect impressions made by the tools, making them unique as well. • Other factors are oxidation or rusting of tools and uneven sharpening.
- 11. TOOL MARK EXAMINATION All crime-scene investigators approach an investigation methodically and carefully. Tool mark evidence includes the mark left at the scene as well as the tool. The tool may be recovered from the suspect or may have been left at the crime scene or discarded elsewhere. This Photo by Unknown Author is licensed under CC BY- NC-ND
- 12. DOCUMENTING THE EVIDENCE • The best way to document tools and tool mark evidence is to use photography. • All evidence is photographed with a measuring device to show the appropriate scale for reference. Photographing Tools • When photographing a tool, experts focus on any scratches or gouges on the surface. • Oblique lighting is preferred to direct lighting because it casts shadows and highlights details that are not easily visible under direct lighting. • Magnesium smoking is often used on dark- colored tools. In this method, magnesium ribbon is burned, which produces a white, powdery film of magnesium oxide that coats the surface of the tool. Coating the tool highlights the detail during photography.
- 13. Photographing Tool Marks • While photographing and recording the tool mark evidence, the expert searches the surface of the tool mark for bits of foreign material using oblique lighting. Example : If the surface is painted, the expert records if any paint was chipped away and provides a description. Tracing Tool marks can be traced on a tracing paper. This helps in comparing the class characteristics. This Photo by Unknown Author is licensed under CC BY-NC-ND
- 14. CASTING IMPRESSIONS The crime scene investigator may actually cut a part from the door or door jamb that contains tool mark evidence. If this is not possible, casting is a commonly used method of preserving impressions of the tool marks. The cast impression will retain the unique indentation marks made by a specific tool. Plastic/rubber, plaster of Paris, dental cast, metal casting, cellulose acetate dusted for fingerprints (magnetic dusting powder and silicone material ) the size of the impression This Photo by Unknown Author is licensed under CC BY- SA
- 15. Taking test impression The material for test impression must be soft soft enough so that the tool edge will not be altered (modeling wax ) When the original mark is in wood, paint or soft metal, hard metal such as steel or brass the standard should be made with a similar material. In cases involving wire cutters the test tool marks can be cable made from copper or aluminum. Several test impressions should be made at various angles with the tool.
- 17. Comparison of tool marks A tool mark must be compared with tool mark, mould with mould and photograph wit photograph having same magnification. The comparison is best done by using comparison microscope and with oblique illumination. Magnification of test and crime sample should be identical. This Photo by Unknown Author is licensed under CC BY
- 18. Source: RG Nichols 2000 Source: RG Nichols 2000 Comparison of tool marks
- 19. Source: RG Nichols 2000 Source: RG Nichols 2000 Comparison of tool marks
- 20. Conclusion for Toolmark Examination • Exclusion • Identification • Inconclusive
- 21. F O RENSIC S CI ENCE UG S E M ESTER V FORENSIC PHYSICS AND BALLISTICS
- 22. This Photo by Unknown Author is licensed under CC BY-SA
- 23. COLLECTING AND PRESERVING A SAMPLE • All evidence is carefully transported to the forensic laboratory to protect it from damage. • When tools are found, they are collected and packaged separately in containers or boxes and then taken to a laboratory for analysis. • The object containing the tool mark or the actual impression cast is also packaged in a container or box and taken to the laboratory. • Small objects may be wrapped with clean paper and placed in small containers or plastic bags, while larger objects can be packed in cartons or boxes. • All evidence must also be correctly labelled and processed.
- 24. Photo 1-2 Pipe with tool marks. The spacing between tool marks on the pipe is 4 mm apart. Case 1 - Pipe and Vise Grip Arson Investigation Evidence Submitted: Evidence collected at the scene of a possible arson investigation. One vise grip Request: Could the vise grip obtained from the suspect’s auto been recently used to loosen the two sections of gas pipe found at the scene of a suspected arson?
- 25. Spacing between teeth tool marks on the pipe are 4 mm apart.
- 26. Case 2 – Gas Explosion Homicide Investigation A landlord had been unsuccessfully trying to evict an old woman from her rent controlled apart for years. A gas explosion occurred at the location and the old woman was killed. The arson investigator suspected foul play, obtained two search warrants, and searches the building’s basement and the landlord’s home. Evidence Submitted: Two sections of gas pipes (building’s basement where the explosion ) and (landlord’s basement)of gas pipes with apparent tool marks . Request: Determine if the tool marks on the known gas pipe (K-2a) were consistent with the tool marks present on the questioned gas pipe (Q-1a).
- 27. Photo 5-1 Two gas pipes, one (Q-1a) from the scene of a homicide and gas explosion investigation, and one gas pipe with known tool marks made with a wrench from the landlord’s basement (pipe marked K-2a).
- 28. Photo: Comparison microscope photomicrograph showing one tooth mark on the K-2a pipe overlapped with one tooth mark on the Q-1a pipe (accidental striation) Photo : comparison of the linear and angular dimensions (Steriomicrope Observations)
- 29. This Photo by Unknown Author is licensed under CC BY-SA
Editor's Notes
- A tool is defined as an instrument that is designed to gain a mechanical advantage. It is also commonly thought of as being the harder of two objects that, when brought into forcible contact, will produce a mark on the softer object. Toolmark is Defined as a mark produced by a tool when that tool is brought into forcible contact with a surface against which the harder tool is used. Class characteristics: Measurable features of a tool that indicate a restricted group source. They are design features of a tool and are therefore determined before manufacture. Such features include size, the profile of the tool, the type of mark to be expected using the tool, and, sometimes, the direction of travel. Specific examples of class characteristics include the width of a screwdriver blade, the jaw width along with the number and spacing of serrated teeth on the jaws of a pipe wrench, and whether a cut is produced by two blades passing over each other such as the case with scissors or two blades cutting and pinching an object such as when bolt cutters are used. Individual characteristics Those features are produced by the random imperfections and irregularities of tool surfaces against an object. These imperfections and irregularities are produced incidental to manufacture and are not intended by the manufacturer. They can be microscopic or large, such as when a portion of the tool surface breaks.