The impressions made by a tool when it comes into contact with a surface are known as tool marks. Depending on the type of impression, its shape, and how the mark was created, these tool markings exhibit a variety of features. The tool markings are classified into different categories based on the force with which they were applied. In the discipline of criminalistics, examining tool markings is significant because it can directly establish a link between a tool mark and the tool that made it. These impressions also help to reconstruct the crime scene.
A tool is a hard object which when forcefully comes into contact with another object, leaves a mark on the softer one like a screwdriver, plier, or an arm joint plier, hammer, and wire cutters, etc.
A tool mark is defined as an impression left by a tool when it comes into contact with a surface. If the tool contacts the surface with a large force, it leaves behind an indentation and the pattern of the tool is permanently reproduced on the surface. These marks play a very vital role in forensic science as the criminals tend to use tools for committing burglaries or other heinous crimes such as cold-blooded murders.
For example, if a burglar tries to enter a house by breaking the lock with the help of a screwdriver, the marks left by the tool are direct evidence of the presence of that tool at the crime scene. But, if the tool is found with a suspect or even near the suspect, it provides a direct link between the suspect and the crime scene. In the field of forensic science, the tool marks can either take the form of negative impressions or abrasion, or both.
A culprit usually uses the same set of tools in the commission of similar types of crimes. If tools marks from various crimes are compared and found identical, the crimes can be linked. Tool marks are, therefore, of great importance in a criminal investigation.
History of Tool Marks
A historical understanding of the tool mark has recognized that marks can be linked directly to tools for many centuries, but there are few recorded references on this specific issue. The use of diverse wound shapes caused by cutting tools such as sickles was discussed in China in the twelfth century, but there is no evidence of their importance even in China.
Henry Goddard (1800–1883) of Scotland Yard is credited with becoming the first investigator to collect forensic evidence from a murder scene by examining a bullet and its associated pattern. A fault was detected in a bullet retrieved from the autopsy victim’s body in 1835, and it was traced back to the original mold from which the bullet was produced. Hans Gross wrote “Handbuch für Untersuchungsrichter als System der Kriminalistik” in 1891, which outlined all of the essential procedures for analysing tool marks.
In 1953, the renowned criminalist Paul Leland Kirk (May 9th, 1902 – June 5th, 1970) wrote a popular book entitled “Crime Investigation” textbook that explains the need for cast marks found in crime scenes if the item with the mark cannot be transported to the laboratories and makes a clear distinction between “compression marks” and “sliding marks.” In his book, he used macrography to evaluate immersed marks, while a comparative microscope was used to examine striated marks, as well as a physical examination.
John E. Davis, a notable criminalist and the chief of the Oakland Police Department’s Criminalistics Division, published ‘An Introduction to Tool Labels, Weapons, and the Striagraph’ in 1958. (Crime Lab). This textbook also presented the “Striagraph,” a novel advanced piece of research equipment capable of calculating, tracing, and recording microsurface contours and serving as a predecessor to advanced laser and digital imaging techniques for future bullet surface scanning technologies.
In 1969, the Association of Guns and Tool Mark Examiners (AFTE) was created in the United States as a non-profit organization dedicated to assisting in the identification of firearms and tool markings.
Characteristics of Tool Marks
They have two different kinds of characteristics:
- Individual ·
The type of impression, its overall shape, and its proportions are all examples of tool mark features. These are usually the general qualities that a criminal investigator can use to figure out what type of tool made the impression and how it was made. However, this accomplishes nothing in terms of identifying the particular tool that made the mark. If only the class characteristics had been accessible, it would have been impossible to tell which tool among a pack of similar tools left an impression.
For this, individual characteristics are taken into consideration. ·
Individual characteristics are microscopic qualities that refer to the small, unusual aspects that a tool exhibits that are unique to that tool. Small, microscopic ridges and imperfections on the instrument itself are examples of these traits.
For example, the tip of a screwdriver is never exactly flat but has irregularities near its edge. These features are created by how the instrument is used and misused, as well as how it is cleaned and maintained. These features allow for formal identification. If such qualities are available on a tool mark, it is feasible to identify the tool used in the crime, even if there are several identical tools.
Nature of Tool Marks
All tool marks can be grouped into two main types, namely compression marks and sliding or crape marks. Sometimes, a combination of these two types may also occur, for example, a hammer blow may leave a compression mark, and at the same time may slide on its edges leaving a sliding mark. Another type of tool mark, sometimes encountered, is the repetitive cut marks, as often caused by saw, drill, or files.
Depending on the force with which a tool comes in contact with a softer surface, Tool marks are divided into three different categories. ·
Impressed Tool Marks
These marks occur when the surface onto which the tool comes in contact, is softer in comparison. When the tool comes in contact with the object (softer than the tool) with a huge force in a motion perpendicular to the plane of the surface leaving an impression on the surface, such tool marks are called impressed tool marks. There is no lateral motion. At the crime scene, the unique imperfections of the tools are transferred to the surface that making possible an identification of the tool involved in the crime. As an example, when a tool like a screwdriver is used by the criminal to forcefully intend a metal surface without penetrating, then the impressions it leaves will help identify the tool.
The sliding contact of the instrument with the receiving surface causes these marks. The imperfections of the tool’s scratching surface cause the surface to be scraped in a specific pattern. Striations are left behind as a result of the marks. The width, depth, and inter-distance vary to a certain extent depending upon the angle of application, the force used, and the relative hardness of the surface. All tools cause such marks that leave compression marks, provided there is a sliding motion. The tools like swords, knives, axes, scissors, chisels, can-openers, screwdrivers, crowbars, pliers, wrenches, spanners, etc. can create sliding marks.
Repetitive Cut Marks
These are the marks left on the recipient surface by the tool’s repeated operation. This class includes saws, hacksaws, files, drills, and other tools. They do not allow for tool identification unless in rare circumstances where the cut mark or hole mark is absent. Examining the repetitive imprints may reveal the type of tool that was used.
The nature of tool marks depends upon the nature of the crime. If trees have been felled and stolen, ax marks may be found on the stamps of the trees. The tool marks will be found at the point of entry, on the locks, safe doors, or the almirahs if a house has been broken open.
If telephone, telegraphic, electric, or traction wires are stolen, the details of the cutting instruments will be found on the cut ends at the scene and on the stolen property.
The stolen parts of vehicles like hubcaps, head-light covers, etc, will carry impressions of nails or bolts. Any object coming in contact with a tool will be able to carry marks of that tool.
Types of Evidence submitted in the case of Tool Marks
There are various types of evidence submitted in tool marks cases include tools like;
- Bolt cutters
- Screwdrivers and chisels
- Knives and box cutters
- Pliers and wrenches
- Crowbars tire irons
- Saws and hammers
Examples of places and surfaces where tool marks can be observed during the investigation:
Some of the places and surfaces where tool marks are likely to be found during the investigation are:
- Window frames
- Sections of metal sheets
- Human bone or a cartilage
- Padlocks and doorknobs
- Bolts and locks, etc.
The analysis of tool marks is divided into several stages. Observe, measure, and explain the tool mark first. The second step is to take a photograph perpendicular to the tool mark. This creates a permanent record of the tool mark’s class and certain unique properties. The toolmark is then cast if the support on which it is positioned cannot be gathered as evidence.
The polymeric dental paste is commonly used to create this cast. The comparison procedure begins when a tool is discovered and its class features match those displayed by the tool mark. The tool is usually seen and photographed. The tool is then used to make comparative tool marks on a soft material to avoid leaving excessive markings on the tool. The procedure of comparison is carried out using a comparison microscope.
Case Study 1
In a murder case an accused pleaded that the victim with a sword attacked him, and he, in turn, threatened the victim with a gun. The blow of the sword struck the barrel of the gun and it got fired killing the victim. He pointed to the cut mark of the sword on the barrel. The test hits were tried in the laboratory with the sword and the barrel. The gun neither goes off nor leaves a cut mark on the barrel. On the contrary, the sword itself got blunted. When the suspect was confronted with the evidence, he confessed to having created the marks with a kukri, which was verified to be correct. Based on this finding, the suspect was charged with a homicidal offense.
Case Study 2
The body of a girl was found in a jungle. She had been strangled with a thin plastic belt, one end of which had been cut off. The cut ends showed faint but clear striation marks left by the blades of the scissors, which were found in the possession of the suspect. The test marks made with the scissors on the belt produced similar patterns or striations leading to the arrest and prosecution of the accused.