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Toolmarks
Toolmark Nomenclature
| Term | Definition |
|---|---|
| Forensic Toolmark Identification | Scientific discipline that is concerned with the identification of a toolmark to the specific tool used to make it. |
| Forensic Firearm Identification | A specialized area of toolmark identification dealing with firearms. A firearm is simply a collection of tools designed to work together to perform a special function. |
| Firearm vs. Toolmark ID Theory | The principles and theory of the science behind firearm and toolmark identification are the same for both areas. |
| Tool | An object used to gain a mechanical advantage. Also thought of as the harder of two objects which when brought into contact with each other, results in the softer one being marked. (Ex: pistol, boltcutter, screwdriver, drill, punch) |
| Tool Working Surface | The working surface is the part of the tool that actually produces the toolmark that is subsequently examined. May not necessarily be the part of the tool that was intended (designed) to be the working surface by the manufacturer. |
| Plastic Deformation | Applied stress that exceeds the elastic limit of a metal, wherein the structure does not return to its original condition upon the removal of stress. (Ex: Bend a coat hanger and try to put it back into its original shape or indent in writing paper) |
| Striation | Contour variations on the surface, generally microscopic, of an object caused by a combination of force and motion when the motion is approximately parallel to the plane being marked. |
| Impression | Contour variations on the surface of an object caused by a combination of force and motion where the motion is approximately perpendicular to the plane being marked. |
| Striated Toolmark | Marks produced when a tool is placed against another object and with pressure applied, the tool is moved across the object producing a striated mark. Friction, Abrasion, and Scratch marks are common terms referring to striated marks. |
| Impressed Toolmark | Marks produced when a tool is placed against another object and enough force is applied to the tool so that it leaves an impression. The class char. (shape) can indicate the type of tool used to produce the mark. Also called compression marks. |
| Class Characteristics | Measurable features of a specimen which indicate a restricted group source. The result from design factors, and are therefore determined prior to manufacture. (Tool width, length, # of serrations, tool shape, tool type, tool action) |
| Subclass Characteristics (1 of 3) | Discernible surface features of an object which are more restrictive than class characteristics in that they are: 1. Produced incidental to manufacture. May occur on a series of sequentially manufactured items. |
| Subclass Characteristics (2 of 3) | 2. Are significant in that they relate to a smaller group source (a subset of the class to which they belong). |
| Subclass Characteristcs (3 of 3) | Can arise from a source which changes over time. |
| Subclass characteristics are manufactured toolmarks that: | Repeat virtually unchanged from one manufactured item to another and can be mistaken for individual (unique) characteristics. |
| Subclass characteristics near the working surface of a tool... | Although subclass toolmarks may be present near the working surface of a tool, they may, either because of their position or the manner in which the tool is normally used, have no influence on the individuality of toolmarks made by the working surface |
| Accidental Characteristics | 1. An event that occurs once but is not reproducible. 2. Formerly used synonymously for individual characteristics. (ex: debris that is lodged into a barrel) |
| Individual Characteristics | Marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. |
| Individual Characteristics - How unique? | They are unique to that tool to the practical exclusion of all other tools. (grinding, sawing, use or damage) |
| Practical Impossibility | Cannot be expressed in mathematical terms, describes an event that has an extremely small probability of occurring in theory, but which empirical testing and experience will not occur. |
| Practical Impossibility in the context of Firearm and Toolmark Identification, means that no firearms or tools other than those identified in any particular case will be found that produce marks exhibiting sufficient agreement of identification because of | 1) Extensive empirical research and validation studies 2) the cumulative results of training and casework examinations that have either been performed, peer reviewed, or published in peer-reviewed forensic journals |
| Why is it hard to do statistical study on toolmark identification? | Tools change everyday, making them more and more individual. |
| Pattern Matching | The act of visually comparing the surface contours of two or more striated or impressed toolmarks for corresponding and/or differentiating features. |
| What is Toolmark Identification? | A discipline of forensic science which has as its primary concern to determine if a toolmark was produced by a particular tool. |
| Value of Toolmark Evidence | 1. Determine if there is a link between suspected tool(s) and questioned toolmark(s) 2. Can only determine if the suspected tool made the questioned mark, not who used the tool to make the mark. 3. All part of the Forensic Triangle and Locard's Exchange |
| Value of No Tool Cases | 1. Provide investigative leads 2. Determine if multiple scenes are linked 3. Determine type and number of tools used 4. How tool was used, direction of tool, if the marks reproduce. 5. Elimination of the tool as a course of the evidence toolmark |
| Tool Class Characteristics (3) | 1. Design Type : What kind of tool is it? 2. Size or specifications: SIze of tool can be important (screwdriver, boltcutters). 3. Configuration: Tool action and how is the tool intended to be used. and what are some unintended ways the tool can be used |
| Tool Individual Characteristics can come from: | 1. Manufacturing 2. Wear from Use 3. Abuse |
| Compression Tool | Tool designed to impress or compact by pressure or striking (ex. hammer, die stamps) |
| Slicing Tool | Tool with at least one sharp (tapered) blade designed to cut by moving in the direction of the cut. (Ex: knives, razor, axe, hatchet) |
| Crimp Tool | Tool with a pair of interactive blades on the same plane, i.e. opposing, that are designed to bend, crease or press together. (Ex: Wire Crimps) |
| Flat Tool | Bladed tool, either squared or tapered, usually designed to pry or perform a special function. (Ex: Tire iron, screwdriver, pry or wrecking bar) |
| Grip Tool | Tool with a pair of interactive jaws on the same plane, i.e. opposing, that abut each other and are designed to grasp or squeeze. (Ex: Vises, pipe wrench, pliers) |
| Pinch Tool | Tool with a pair of interactive jaws on the same plane, i.e.opposing, that abut each other and are designed to cut. (Boltcutters, nippers, diagonal cutter) |
| Shear Tool | Tool with a pair of interactive jaws on the adjacent planes, that pass by each other, and are designed to cut. (Scissors, tin snips, pruners) |
| Documentation | -Maintain COC - Basic Description of tool and toolmark -Presence of trace evidence -Photo documentation, sketches, narratives -Tool working surface: class, potential subclass, and ind. charac. -How was the tool used that made the mark? |
| Why document what we do? | 1. Refresh memory 2. Shows what you did, how you did it, and what conclusions were reached 3. Support conclusions in report 4. Notes must show you followed lab protocols, used generally accepted practices, and stayed within your area of expertise. |
| How to Take Notes | Notes should be written such that another examiner could review them and know exactly what you did and how you did it with no gaps. Very organized, methodical notes are essential in toolmark cases that involve multiple working surfaces |
| Trace Evidence Examples | 1. Paint 2. Blood 3. Glass 4. Hair 4. Fibers 5. Building materials 6. Any traces of material from object(s) on which the tool has been used. |
| Generation of Test Toolmarks | 1. Always use soft material first (lead) 2. Try to recreate the toolmark with the same pressure, angle, directions, etc. 3. Always compare tests for reproducibility 4. If necessary, make test in same material as evidence; save every test. |
| Casting toolmarks | Optimum way to preserve toolmarks on objects that are not practical to recover from a scene. A cast may help with reflectivity issues A toolmark is a negative impression of the tool's working surface |
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