Forensic analysis of tool marks
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Tool marks evidence plays an important role in forensic science. Tool marks are impressions or marks left on surfaces by tools and can be used to identify the specific tool that made the mark. There are different types of tool marks such as impressions, abrasions, cuts, and drill holes. Tool marks contain both class characteristics common to groups of tools and unique individual characteristics. Tool marks are collected using methods like photography, casting, and test marks. Examiners compare both class and individual characteristics of tool marks using various techniques like microscopy and superimposition to determine if two marks have a common origin.
Forensic analysis of tool marks
- 1. Tool Marks Examination and Evaluation Suryakant Mishra Asst. Professor Department of Zoology & Forensic Science Kurukshetra University, Kurukshetra
- 2. Introduction : A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. For example, a screwdriver or crowbar could produce tool marks by being impressed into or scraped along the surface of another object. Tool marks Fig: A flat-bladed screwdriver
- 3. Tool marks play a very vital role in forensic science, as the criminals have a tendency to use tools for committing crimes such as Burglaries and theft Murders Vehicle accidents Death due to firing Fig: bullet holes and deep sliding marks on car
- 4. Types of evidence submitted in tool marks cases include tools like: Bolt cutters Screwdrivers and chisels Scissors Knives and box cutters Pliers and wrenches Crowbars tire irons Saws and hammers Firearms
- 5. Basis of tool marks identification: Law of individuality Locard’s exchange principle Permanency
- 6. Tool marks have two different kinds of characteristics: Characteristics of tool marks Class characteristics: Common to a group of objects General Shape • General Dimensions • Do not permit identification of exact tool used Example: A hammer has a characteristic dimensions length and width Individual characteristics: Unique to a given object (microscopic nature) Example: indentations, defect marks , striations marks
- 7. Type of Tool Marks : 1. Impressed marks The first type is an impression which is a negative reproduction of the tool surface, As a tool hits a softer surface, the shape of the tool and imperfections in its surface may be left behind as an impression. such as screw driver or pry bar impressions left on windows or punch impressions on safes or : crow bar into wood
- 8. 2. Abrasions/ scraps or striations marks: Caused when a tool slides or scratches across another surface which produces striated areas on the marked surface. Occasionally impressions made by tools with striated surfaces may resemble in appearance abrasion or friction marks Example: sliding a screw driver along the side of a car surface
- 9. 3. Cutting (“crushed”) marks: Caused by pressure being applied to both sides of an object Examples: pliers or wire cutters 4. Repetitive cut marks Caused by repetitive actions Example: a saw marks 5. Drill holes Fig: repetitive cut marks (saw marks)
- 10. Collection of Tool Mark Evidence Step 1: Collection and recording of tool marks form crime scene : a. Photography: b. Casting methods of tool marks collection Plaster of Paris Plasticine Latex and plastic solution Dental stone Wood metal Adhesive tape
- 11. Two types of photographs are needed for courtroom identification. • An over-all photo depicting the entire object which bears the toolmark. • A close-up photo showing the detail of the toolmark. This close-up is for identification and orientation only and cannot be used for actual comparisons. • Photograph of tool marks should be taken with scale
- 12. Sharps packaging The operating surfaces of suspect tools should be protected and preserved. The tool should be individually packaged and identified with a string tag bearing the information required by agency crime scene search protocols. If a tool is a sharp, especially a potentially body fluid-contaminated sharp, it should be packaged in a leak proof, puncture-resistant, sealed container. Source: https://projects.nfstc.org/firearms/module06/fir_m06 _t06_05_f.htm
- 13. Plastic containers are generally useful for packaging evidence because they can be sealed closed and permit observation of the contents. However, they must not be used for packaging of biological evidence. Biological evidence, such as blood-stained clothing or vegetation suspected to be cannabis, should be packaged in paper containers that allow airflow around the material. Plastic is not recommended for packaging firearms evidence since any moisture present could promote rusting of the item.
- 14. Step 2: Make test marks with the suspected tool for comparison purpose: Similar surface material where tool mark was present preferably used for collection of standards or Make a cast of the marks, usually with silicone rubber. Comparison process: 1. Comparison of class characteristics- such as dimensions, shape, length and width, depth. 2. Comparison of individual characteristics.
- 15. Examination and matching of tool marks: 1. Mechanical fit 2. Comparison microscope 3. Stereomicroscope 4. Striagraphy 5. Superimposition
- 16. Fig: Comparison microscope Fig: stereomicroscope
- 17. Comparison and matching of tool marks: 1. Physical match: mechanical fit 2. Side by side match 3. composite match 4. Superimposition
- 18. Fig: Side by side matching of fired cartridges base marks A comparison microscope is used to perform the comparison process. The unknown tool mark is placed on the left side of the microscope and the known mark on the right side. If individual characteristics of both tool marks match, the common origin between the unknown tool mark and the tool is established.
- 19. Figure: composite match of striations marks on fired bullets
- 20. Comparison photomicrograph of test sledge hammer mark on lead (left) and hammer mark on burglarized safe dial (right).