Discuss The Importance Of Examination Of Toolmarks At A Crime Scene

The importance of examining a crime scene lies in the fact that the investigators need to establish what exactly happened and who is the person that needs to be held responsible for it. It is often done to solve and prosecute violent crimes as well as to determine the full extent of the crime scene. The examination of the scene constitutes a lengthy and arduous process, often requiring experienced personnel from different fields in addition to the investigating officers.^[5] There is a presence of different kinds of evidence at the crime scene, some of them including fingerprints, bodily fluids, DNA evidence, toolmarks, impressions, etc.^[6] The most important of these to our analysis are the toolmarks and the relevance of their presence and examination at a crime scene. Crime scenes involving tool marks often cover a broad range of offenses and hence, require the study of various disciplines.

Toolmarks

In the context of a toolmark, we can understand a tool as a “device or implement, especially one held in the hand, used to carry out a particular function”.^[7] It extends or betters a person’s ability to change or modify his surroundings. When we talk about a crime scene, a criminal tool is a tool that aids in the commission of a crime. Criminal offenses often involve tools such as knives, crowbars, slim jims, hammers, etc.^[8] Locard’s Principle of Exchange suggests that whenever there is contact between two objects, there are going to be certain traces that will be left behind as a result of that contact. This principle not only highlights that even the smallest of marks left behind at the crime scene can help in the reconstruction of the crime,^[9] but that the examination of evidence at the crime scene must be done with the utmost care.^[10]

Toolmarks are one such evidence that are analyzed as a part of the examination of a crime scene.^[11] Henry Goddard was one of the first people to collect evidence with respect to a toolmark by analyzing a bullet during a murder investigation.^[12] In simple words, toolmarks are the scratches or impressions or indentations that are left behind by tools at the scene of crime. They can either be caused when a hard tool leaves an impression on a softer surface/object or when a hard tool scrapes across another hard surface/object or when a tool cuts across. Certain tools leave behind certain types of toolmarks and it is this characteristic that makes them important in the examination of a crime scene.^[13]

Examination Of Toolmarks

The examination of impressions created by toolmarks is crucial to recreate the crime scene;^[14] it plays a significant role in establishing a link between a tool mark and the tool that made it, besides assisting forensic investigators identify distinctive patters and match them with their respective marks.^[15] The entire process of toolmark identification resolves around firearms identification, fracture matching/ physical fit, impression or a striation, depending on the nature of tool mark.^[16] Thus, based on the velocity and force with which an instrument hits the corresponding surface, tool marks have been classified into three distinct categories.

• Impressed Tool Marks- When a tool perpendicularly hits a comparatively softer surface; it tends to leave an impression provided that the force applied is not lateral in motion. During investigation, such unique impressions are collected and transferred to such probable surfaces that facilitate the identification of the tool involved in the crime. For instance, if a criminal uses a screwdriver to break and penetrate inside the house, it will leave behind certain impressions on the lock indicating the use of such a tool.^[17]
• Sliding Marks- At a stationary position, when two instruments slide through each other, brushing against one another, signaling uninterrupted flow of energy through contact; results in the creation of these marks. These impressions leave behind unique patters on the scraped surface, which is scrutinized carefully by the forensic experts with respect to its width, depth, distance, force and angle of application. Usually, metallic tools such as knives, axes, screwdrivers, wrenches and spanners create such sliding marks.^[18]
• Repetitive Cut Marks- In an operation, when a particular tool is repeatedly used, it blots a permanent dent on the recipient surface. It categorically includes files, hacksaws, drills etc. Only under exceptional circumstances wherein cut marks or hole marks aren’t present, tool identification is processed to reveal the nature and type of tool used in inflicting injuries or committing the alleged crime.^[19]

At a crime scene whenever a tool mark is found, the investigating authorities have to follow a prescribed procedure. Firstly, at least two photographs have to be taken, one depicting the background of the impression and other one should be the close up of the caricature.^[20] Secondly, the officer is obligated to use a tracing paper to get hands on the exact dimensions of the tool mark, this step is crucial, as it facilitates in comparing class characteristics. Once the object is traced a negative three dimensional image of an impression is to be casted or molded using either plastic or rubber material. This eliminates the possibility of excluding fine details of the tool marks.^[21] In exceptional circumstances wherein a considerably large size of impression is to be casted upon, plaster of paris or calcium sulphate in its hydrated form can be used once talcum powder is sprayed overthe surface of tool marks. Moreover, to enhance its rigidity, experts spray shellac dissolved in alcohol to secure its surface details.^[22] Alternatively metals casting can also used. The most suitable amongst all is the wood metal because of its unique composition and characteristics. By weight its 50% bismuth, 25% lead, 12.5% tin, 12.5% cadmium which helps it melt at 71 degrees celsius.^[23] Marks from concrete objects such as stones, arrows, buckles, chokers etc can be lifted by any anetone dissolved with cellulose acetate. However, it should be photographed, scaled and imprinted immediately otherwise the layer will shrink. Once the suspected tool is collected it’s sent to laboratories for examination under stereo microscopes, they detect minute metal, wood and foreign articles present on the tool, to compare it with the surface on which the impression was found.^[24]

Importance Of Examination Of Toolmark At Crime Scene

The primary objective behind examination of tool marks is to ascertain whether the disputed mark has been created by a specific tool.^[25] Critical and careful observation of these tools helps reveal its description, class characteristics, size, and manner in which the tool was used to harm an individual or commit an alleged offence.^[26] Secondly, the advancements in the examination of toolmarks have resulted in accurate and highly detailed identification of the origin of toolmarks. Tools often play a crucial role in the commission of offences and accuracy in the identification of the marks that they leave behind would bring the investigator one step closer to the perpetrator.^[27]

The examination of toolmarks at a crime is a multi-disciplinary process and primarily involves the identification and analysis of the marks or impressions left behind by tools at the crime scene. The rise of forensic databases and technology has helped the forensic experts to employ a wide range of methodologies in ascertaining the origin of a toolmark at a crime scene. Toolmark examiners are often tasked with employing complex and complicated processes to analyze toolmarks. Examination becomes even more important considering the significance of toolmarks at a crime scene. One of the main objectives of the examination of a crime scene is to reconstruct the offense and toolmark examination brings investigators one step closer to achieving this objective. The principle that tools used to commit offenses leave behind certain characteristic marks or impressions in accordance with Locard’s Principle of Exchange has been primarily responsible for the development of this branch of forensic science. A forensic examiner is not just aware of the distinct objects left behind by each tool, but is also well aware of the manufacturing process that produces such a tool, which is another characteristic unique to the tool. Hence, the importance of toolmark examination at a crime scene lies in the fact that there is a uniqueness attached to each tool and when a tool is employed to commit an offense it is bound to leave behind a mark which eventually helps in the reconstruction of a crime.

The authors are students of Symbiosis Law School, Hyderabad and also interns at Livelaw. Views are personal.