**4. Types of tool marks**

Generally, there are three categories of tool marks left by tools on the surfaces they hit. These impressions are produced by the possibility of a compression action, sliding action or cutting action occurring.

A compression impression: Probably the most common and most negative representation of the surface of the tool, caused by pressure, blow or gouge of the tool on the surface of a wood, metal or other surface. Compression is imprinted on softer material when tool surface presses against its surface [14]. For instance,

a screwdriver is most often used to tighten or loosen screws. However, if it is used to pry open a widow, it will leave impressions in the windowsill.

Friction marks (sliding action): The second type is a mark of abrasive wear or resistance left by the tool's sliding or chopping action that creates striations on a marked surface. Friction marks are fine parallel striations and are a characteristic feature left by a tool scraped across a smooth surface, such as dressed wood or metal. It is common to focus on such striations when making bullet and tool mark comparisons. Parallel lines have the potential to be matched using microscopic comparison. There are an infinite number of ways to apply a tool to a surface, and the resultant striations are the effects of every variation. For example, when a crowbar is forced into the area between a door and the front part of the door to force the door wide open, pressure is applied to the tool handle. An abrasion or friction mark is created by forced application of the crowbar. The majority of bull cutter marks on rods or wires, screwdriver scratch marks and knife or axe cut marks are examples of friction mark markings.

Cutting edges are not as commonly used in the commission of crimes as prying tools with blunt edges, so finding marks of cutting tools is not frequent. There is a high significance in cut marks being positively identified with the tool producing them. A cutting impression is a combination of these two impression types, as is found in scissors.

From these three tool mark impression types, both the class and individual characteristics of the tool can be identified; for instance, marks left on a doorway from a pry bar can be matched back to that specific pry bar.

During tool mark analysis, the analyst may discern what type of tool made a particular mark, and whether a tool in evidence is the tool that made it. The tool mark can also be compared to another tool mark to ascertain if the marks were made by similar, or the same, tools.

#### **5. Types of tool marks comparison**

A well-known and extensively used forensic methodology is the comparison of tool marks, which is typically regarded to provide convincing trial evidence and facilitate the investigation of a crime. However, there is a great deal of ambiguity as to the uniqueness of such marks and, in particular, the probability of more than one tool replicating a mark. According to Houck and Siegel [15, 16], tool mark examiners need to have a conceptual understanding of how to produce and machine a variety of tools. Limitations on comparative forensics have initiated the need for an objective, as each tool has specific surface characteristics for the identification of tool marks to facilitate scientific research. In 2009 National Academies report, researchers recommend reinforcing the scientific justification for the standards and specifications for the tool mark identification in forensic science.

The forensic principle of comparison explains that only the like can be compared with the notion of comparison. It reinforces the need for samples and specimens to be included for comparison with the objects in question. Therefore, the prime purpose of forensic comparison is to establish which characteristics and specifications of the samples in question obtained from the crime scene (including a tool or a population of reference items, screw bag or plastic bag roll) varied or directly correlate with those obtained from the source on the control item. Comparing features, however, is a deceptively simple process, but understanding what the outcome implies is much more difficult if one does not understand exactly what the characteristics and specifications are or how they were acquired.

**93**

completely.

examination:

*Forensic Analysis and Interpretation of Tool Marks DOI: http://dx.doi.org/10.5772/intechopen.98251*

Another challenging part of a comparison is to examine the manufacturing patterns associated with the "control" object. The manufacturing process leaves distinctive microscopic striations on the tool's operating surfaces as the marks produced depend not only on the type of tool being used but also on how it is used (as a hammer, or lever or force exerted), the contact position (leading angle or trailing

There are three categories of features that an examiner will need to identify:

• Class features: A combination of features that facilitate the positioning of the sample in a class of related material properties. Champod et al. [17] state that the class characteristics of a tool are usually unique and macroscopic; for example, class characteristics of firearms are correlated with the tensile strength of the weapon and projectile or cartridge steel and the rifling in the

• Subclass features: Attributes that are not specific to a particular object but provide some discriminatory practices among groups of tools with features of the very same class. They appear during processing but are not necessarily introduced. Over time, the reference of subclass functionality can evolve. Nichols [4] explains what qualifies a characteristic as subclass: "If one were to examine a cast of the bore of a firearm, such characteristics would have to exist for the entire length of the cut surface. If a certain characteristic appeared after the cut surface had already started, then it would be an imperfection caused by the current process. If it disappeared before the end of the cut surface, then it is gone and by definition of its absence cannot be passed onto the next cut surface. Therefore, the only characteristics capable of being defined a subclass

would be those that persist for the entire length of the cut surface."

• Individual/unique characteristic: Individual characteristics relate to the specific characteristics of both the questioned samples and the reference samples, which share a similar origin with a high degree of reliability. Examples of evidence possessing individual characteristics are fingerprints, tool marks and

Therefore, in order to analyze the results, it is imperative to understand the sets of features and details generated during the production process and then use, how they will be portrayed in a mark and how to differentiate between the different types, as this will determine what you can say about the comparison. The quality of the situation mark in a mark comparison is always the main limitation. Information that may have been visible on a tool may not have been replicated in a mark for certain variables, such as the physical parameters of the material. If they are considerably weaker than the tool, the information of interest cannot be replicated

However, occasionally, the difference will be significant and on occasions may even be to the extent that one expert will say the tool was responsible and the other that it was not the tool. Occasionally, while the difference is apparent, it may be to the degree that one analyst states that the tool was accountable and the other that it was not the tool. With all this perspective, the importance of the independent critical results test of a secondary tool mark expert should not be overlooked. However, this is not always necessary, and in order to settle the debate, a third expert may be

AFTE Theory of Identification (1998) classified four categories of tool

angle) and other factors that may help to identify the metal tools [16].

firearms barrel that is transferred to the bullet.

markings on bullets.

required to conduct a verification.

*Forensic Analysis and Interpretation of Tool Marks DOI: http://dx.doi.org/10.5772/intechopen.98251*

*Forensic Analysis - Scientific and Medical Techniques and Evidence under the Microscope*

pry open a widow, it will leave impressions in the windowsill.

friction mark markings.

made by similar, or the same, tools.

**5. Types of tool marks comparison**

found in scissors.

a screwdriver is most often used to tighten or loosen screws. However, if it is used to

Friction marks (sliding action): The second type is a mark of abrasive wear or resistance left by the tool's sliding or chopping action that creates striations on a marked surface. Friction marks are fine parallel striations and are a characteristic feature left by a tool scraped across a smooth surface, such as dressed wood or metal. It is common to focus on such striations when making bullet and tool mark comparisons. Parallel lines have the potential to be matched using microscopic comparison. There are an infinite number of ways to apply a tool to a surface, and the resultant striations are the effects of every variation. For example, when a crowbar is forced into the area between a door and the front part of the door to force the door wide open, pressure is applied to the tool handle. An abrasion or friction mark is created by forced application of the crowbar. The majority of bull cutter marks on rods or wires, screwdriver scratch marks and knife or axe cut marks are examples of

Cutting edges are not as commonly used in the commission of crimes as prying tools with blunt edges, so finding marks of cutting tools is not frequent. There is a high significance in cut marks being positively identified with the tool producing them. A cutting impression is a combination of these two impression types, as is

From these three tool mark impression types, both the class and individual characteristics of the tool can be identified; for instance, marks left on a doorway

During tool mark analysis, the analyst may discern what type of tool made a particular mark, and whether a tool in evidence is the tool that made it. The tool mark can also be compared to another tool mark to ascertain if the marks were

A well-known and extensively used forensic methodology is the comparison of tool marks, which is typically regarded to provide convincing trial evidence and facilitate the investigation of a crime. However, there is a great deal of ambiguity as to the uniqueness of such marks and, in particular, the probability of more than one tool replicating a mark. According to Houck and Siegel [15, 16], tool mark examiners need to have a conceptual understanding of how to produce and machine a variety of tools. Limitations on comparative forensics have initiated the need for an objective, as each tool has specific surface characteristics for the identification of tool marks to facilitate scientific research. In 2009 National Academies report, researchers recommend reinforcing the scientific justification for the standards and

from a pry bar can be matched back to that specific pry bar.

specifications for the tool mark identification in forensic science.

The forensic principle of comparison explains that only the like can be compared with the notion of comparison. It reinforces the need for samples and specimens to be included for comparison with the objects in question. Therefore, the prime purpose of forensic comparison is to establish which characteristics and specifications of the samples in question obtained from the crime scene (including a tool or a population of reference items, screw bag or plastic bag roll) varied or directly correlate with those obtained from the source on the control item. Comparing features, however, is a deceptively simple process, but understanding what the outcome implies is much more difficult if one does not understand exactly what the characteristics and specifications are or how they

**92**

were acquired.

Another challenging part of a comparison is to examine the manufacturing patterns associated with the "control" object. The manufacturing process leaves distinctive microscopic striations on the tool's operating surfaces as the marks produced depend not only on the type of tool being used but also on how it is used (as a hammer, or lever or force exerted), the contact position (leading angle or trailing angle) and other factors that may help to identify the metal tools [16].

There are three categories of features that an examiner will need to identify:


Therefore, in order to analyze the results, it is imperative to understand the sets of features and details generated during the production process and then use, how they will be portrayed in a mark and how to differentiate between the different types, as this will determine what you can say about the comparison. The quality of the situation mark in a mark comparison is always the main limitation. Information that may have been visible on a tool may not have been replicated in a mark for certain variables, such as the physical parameters of the material. If they are considerably weaker than the tool, the information of interest cannot be replicated completely.

However, occasionally, the difference will be significant and on occasions may even be to the extent that one expert will say the tool was responsible and the other that it was not the tool. Occasionally, while the difference is apparent, it may be to the degree that one analyst states that the tool was accountable and the other that it was not the tool. With all this perspective, the importance of the independent critical results test of a secondary tool mark expert should not be overlooked. However, this is not always necessary, and in order to settle the debate, a third expert may be required to conduct a verification.

AFTE Theory of Identification (1998) classified four categories of tool examination:

