**6. Forensic examination of tool marks**

The purpose of the analysis and comparison of the tool mark is to determine whether a mark or a series of marks in dispute have been made by a specific tool. Careful examination of the questioned tool mark(s) typically offers descriptions of the class characteristics and size of the tool responsible for making the marks in question, if the tool is damaged and how the tool was used to produce the alleged marks [10]. A tool mark analysis primarily initiates with a morphological examination of the tool and its features. For each tool mark, such as branding, cutting, compression, crimping, engraving, firing, etc., Klees [18] therefore suggests a categorization system to enhance the common classification systems found in the literature and to provide a more standard way. Tool mark analysts are objective and conceptual analysts who seek to assess if they are combating a tool mark and a similar tool. They use their results on the basis of their assessment of the evidence. Tool mark examiners collect information about a piece of evidence in order to establish a hypothesis about what occurred, so that it can be linked with certain other observations and results. Tool mark analysts are unbiased and conceptual analysts who aim to determine whether a tool mark and a particular tool are being countered. They employ their conclusions on the basis of their analysis of the proof. In order to create a hypothesis about what happened, tool mark examiners collect information about a piece of evidence so that it can be combined with other information and conclusions.

#### **6.1 Physical matching**

Physical fits, also pointed to as "mechanical fits," can be identified in a massive variety of criminal investigations, even as part of a more detailed instance of the tool mark. A physical fit exam is required when it is imperative to ensure that two or more parts of the product that have been partitioned, broken, cut and often forcibly removed were actually attached or fitted together [19]. Further, Jayaprakash [20] emphasizes on the unique characteristics that make a fundamental paradigm relevant for individualization. Restricted physical comparison literature reviewed

**95**

**6.3 Automated system**

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

evidential justification for individuality [19].

and therefore to form an inference.

been passed or is a function of the contact.

increases the likelihood of positive acknowledgment.

"jigsaw" suits.

order to facilitate a fit.

**6.2 Casting**

that in the course of the trial, the objective scientific reliability and admissibility of

• Broken portions that will potentially be refitted, otherwise referred to as

• Broken items require a thorough tool mark examination such as microscopic comparison and casting in an effort to validate that the parts match together

• Broken, torn or split objects where knowledge of the manufacture and appearance of marks left on the surface of the material must be taken into account in

• Objects that were actually built to fit together were perhaps in touch for a period of time. Typically, these examinations require an analysis of what matter has

Collection, processing and examination of impression and tool mark evidence are one of the major components of forensics. The disadvantages associated with the selection and preservation factors are an unacceptable mix, creating a negative impression of resources and environmental factors. These restrictions relate to lack of detail, compromise of class perception and individualization of features used to position a particular piece of evidence at the scene of a crime. It is necessary to initially make the best cast possible with the inherent destructive potential of impression and tool mark casting. Occasionally, the circumstances of a crime scene impact the availability of casting techniques, contributing to the continuity of a cast [21]. A wide range of casting materials are often utilized to manufacture casts of tool marks: negative molding, low-melting metal alloys (e.g., wood metal) and silicone rubber. The material that most closely fits the specifications of an efficient casting material is silicone rubber. A tool mark's microscopic detail is carefully repeated; it is impact resistant when kept at room temperature and is comparatively cheap. The silicone rubber casting material is supplied as a partly polymerized base with which a catalyst must be mixed in order to allow polymerization. Forensic professionals focus on Microsil Silicone Casting Medium to recreate the subtlest tool markings and impressions. Laboratory studies have shown that they are superior to other established flexible silicone casting techniques by substantially improving the visibility of tool marks, firing pin impressions and latent fingerprint lifts. Microsil

An automated tool mark identification system uses an acquisition method for the processing of 3D data from tool marks left by tools on the sample surface, a signature generation module for the generation of tool mark signatures from the data

Features participating in physical matching and comparing rendered definitive judgments in patterned evidence that eliminate ambiguity during investigation and also an array of measurable units that comprise the entire pattern area, raising the probability of a pattern of verisimilitude known to trigger infinity that provides

such physical comparisons tend to be regarded with skepticism.

Physical fit examinations fall into four main categories:

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

that in the course of the trial, the objective scientific reliability and admissibility of such physical comparisons tend to be regarded with skepticism.

Features participating in physical matching and comparing rendered definitive judgments in patterned evidence that eliminate ambiguity during investigation and also an array of measurable units that comprise the entire pattern area, raising the probability of a pattern of verisimilitude known to trigger infinity that provides evidential justification for individuality [19].

Physical fit examinations fall into four main categories:


#### **6.2 Casting**

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

bullets are found.

appears.

• Identification is the inference that the class traits of two samples appear to be the same and that the individual features are reasonably agreed to conclude that the same weapon was shot. If they agree, for instance, two copper jacketed

• Inconclusive agreement of class characteristics is defined as "the outcome of a comparison in which there is some agreement of individual characteristics and all discernible class characteristics, but insufficient for identification, agreement of all discernible class characteristics due to an absence, insufficient, or lack of reproducibility, agreement of all discernible class characteristics and disagreement of individual characteristics but insufficient for an elimination".

• A substantial disparity between distinguishable class characteristics and/or individual characteristics is triggered by elimination, or exclusion from the analysis. For fired bullet comparisons, an exclusion is usually based on observed

• In the absence of microscopic marks, "Inappropriate for comparative analysis,"

The purpose of the analysis and comparison of the tool mark is to determine whether a mark or a series of marks in dispute have been made by a specific tool. Careful examination of the questioned tool mark(s) typically offers descriptions of the class characteristics and size of the tool responsible for making the marks in question, if the tool is damaged and how the tool was used to produce the alleged marks [10]. A tool mark analysis primarily initiates with a morphological examination of the tool and its features. For each tool mark, such as branding, cutting, compression, crimping, engraving, firing, etc., Klees [18] therefore suggests a categorization system to enhance the common classification systems found in the literature and to provide a more standard way. Tool mark analysts are objective and conceptual analysts who seek to assess if they are combating a tool mark and a similar tool. They use their results on the basis of their assessment of the evidence. Tool mark examiners collect information about a piece of evidence in order to establish a hypothesis about what occurred, so that it can be linked with certain other observations and results. Tool mark analysts are unbiased and conceptual analysts who aim to determine whether a tool mark and a particular tool are being countered. They employ their conclusions on the basis of their analysis of the proof. In order to create a hypothesis about what happened, tool mark examiners collect information about a piece of evidence so that it can be combined with other information and

Physical fits, also pointed to as "mechanical fits," can be identified in a massive variety of criminal investigations, even as part of a more detailed instance of the tool mark. A physical fit exam is required when it is imperative to ensure that two or more parts of the product that have been partitioned, broken, cut and often forcibly removed were actually attached or fitted together [19]. Further, Jayaprakash [20] emphasizes on the unique characteristics that make a fundamental paradigm relevant for individualization. Restricted physical comparison literature reviewed

differences in some of the general rifling properties.

**6. Forensic examination of tool marks**

**94**

conclusions.

**6.1 Physical matching**

Collection, processing and examination of impression and tool mark evidence are one of the major components of forensics. The disadvantages associated with the selection and preservation factors are an unacceptable mix, creating a negative impression of resources and environmental factors. These restrictions relate to lack of detail, compromise of class perception and individualization of features used to position a particular piece of evidence at the scene of a crime. It is necessary to initially make the best cast possible with the inherent destructive potential of impression and tool mark casting. Occasionally, the circumstances of a crime scene impact the availability of casting techniques, contributing to the continuity of a cast [21].

A wide range of casting materials are often utilized to manufacture casts of tool marks: negative molding, low-melting metal alloys (e.g., wood metal) and silicone rubber. The material that most closely fits the specifications of an efficient casting material is silicone rubber. A tool mark's microscopic detail is carefully repeated; it is impact resistant when kept at room temperature and is comparatively cheap.

The silicone rubber casting material is supplied as a partly polymerized base with which a catalyst must be mixed in order to allow polymerization. Forensic professionals focus on Microsil Silicone Casting Medium to recreate the subtlest tool markings and impressions. Laboratory studies have shown that they are superior to other established flexible silicone casting techniques by substantially improving the visibility of tool marks, firing pin impressions and latent fingerprint lifts. Microsil increases the likelihood of positive acknowledgment.

#### **6.3 Automated system**

An automated tool mark identification system uses an acquisition method for the processing of 3D data from tool marks left by tools on the sample surface, a signature generation module for the generation of tool mark signatures from the data collected and an analysis unit for the comparison of pairs of tool mark signatures in order to obtain a numerical similarity value representing their identical characteristics. The process is carried out with the aid of an integrated computer [22].

### **6.4 Databases of tool marks**

A wide variety of different tool marks are found at the crime scene due to the different shapes and surface where the tool mark is rendered. Bolt cutters, wire cutters or crowbars have been used to break a door in many cases of burglary. These tools can produce marks that appear in various patterns: impressions and striation marks. Therefore, the Netherlands in collaboration with the Dutch Police developed a database for tool marks, known as Tool Mark Imaging System Database (TRAX). The device is designed for collection, restoration and comparing of tool images and their textual descriptors' width, kind of tool mark, etc.) [23].

#### **6.5 Known tool marks test impressions**

In practice, the investigator of the tool marks produces negative test tool marks using the suspect tool to compare microscopic surface characteristics between known test tool marks and evidence tool marks. It is recognized that the contrast between a suspected tool and a known test marks is always quicker and more effective than casting or even photography techniques [24]. It is also suggested to use known test tool marks developed in the very same way as the actual tool marks questioned. Traditionally, test tool marks are generated on sheets of soft metal or metal alloy, bars or tubes such as lead, wood alloy and, more recently, lead tape. Firstly, without losing the working surface of the tool, these surfaces are flexible enough to allow test casts with the finest tools. Second, their malleable nature enables the reproduction of the fine scrapes and ridges present on the instrument's working surface in the case of striation marks. Finally, the resulting known test tool marks are accurate, highly detailed, negative impressions of the working surface of the tool [10].

#### **7. Interpretation**

Impressions retrieved from crime scene are compared with reference tools to identify the impressions and to determine if they share a common origin. If there is a good fit between the two impressions, it is necessary to categorize the attributes and explain the probability of it being made randomly or on purpose. In the instance of a negative match between features, a careful investigation is required to determine whether the differences are significant or not and if there is a sensible and fair interpretation that can be made.

The forensic examiners can build a complete probative importance of the decision based on such similar and non-similar findings in order to present it as substantial court evidence. This also demonstrates the examiner's extensive knowledge in explaining and analyzing the fabrication process as well as the tool's wear and tear over time.

The following concerns will arise while an expert is doing a mark comparison.


**97**

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

pressure applied.

**8. Evaluation**

3.This would be a problem if characteristics like pressed lines, milling, and broaching were designed in such a way that they could appear on numerous tools made in a similar way and be indistinguishable from other tools. Similarly, if qualities like grending or damage breakdown were produced at random

4.Extraneous particles detected on the surface of impressions retrieved from crime scenes and at the surface of reference tools may be affected by external factors such as the nature of the substrate, the direction and the amount of

Evaluation is the framework of a conclusive judgment based on analysis and interpretation in significant detail by weighing what the findings mean in reference to the prosecution and the defense statements. There are (at least) three perspec-

1.In one approach, the examiner must make claims that represent the balance of probabilities. The investigator either makes a conclusion about the forensic evidence's reliability based on the balance of likelihoods or makes a judgment about the relative probability of the observed findings under alternative theories.

• The examiner starts by comparing the objects (tools) to see if there are any significant differences that rule out the possibility of a common source. When identifying characteristics are noted, the investigator decides that the

items do not share a common source, a process known as "exclusion."

• When the objects cannot be differentiated (i.e., the likelihood of a common source cannot be ruled out), the examiner then evaluates the rarity or uniqueness of the shared features as a second step. If the examiner believes that the shared features are so unique that they are peculiar (one-of-a-kind), the examiner may infer (and report) that the items are all from the same source—this conclusion is often called individualization or identification. If the examiner believes the shared characteristics are not identical, he or she could state the uniqueness of the related features or the probability that a random tool of the same kind will have them. Similarly, the examiner may claim unequivocally that the artifacts are indistinguishable or that they "play," without mentioning the match's rarity. Eventually, the analyst may

3.In a third approach, the examiner will use numbers (e.g., "there is a 99%

chance this tool mark was produced by the suspected tool") or words (e.g., "it is extremely likely that these marks were made by the same tool") to draw conclusions about the likelihood that the objects have a similar source. These conclusions are sometimes called source probabilities. This third approach is distinguished from both the first (balance of likelihoods) and the second (two-step analysis) approaches in that it allows the examiner to take a position or make judgments about the prior odds that the items being compared have a common source. To put it another way, the examiner's decision must be based on more than an assessment of the physical characteristics of the tools being comparison.

and regarded unique, no other instrument would have them.

tives about how investigators can report their conclusions.

2.The second method necessitates a two-step study.

conclude the comparison inconclusive.

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

