Form follows function: Applying photographic content analysis to forensic firearm identification.

Drawing forensic conclusions from an image or a video is known as "photographic content analysis." It involves the analysis of an image, as well as objects, actions, and events depicted in images or video. In recent years, photographic depictions of objects suspected as illegal firearms have substantially increased, appearing on CCTV surveillance footage, captured by mobile phones and shared on social media. However, the law in Israel states that a person can be charged with illegally possessing a firearm only if it can be proven that the object is capable of shooting with lethal bullet energy. This becomes more challenging in cases where the firearm was not physically seized, and the evidence exclusively consists of images and video. In this study, photographic content analysis was applied to images and video where objects suspected as commercial or improvised firearms had been depicted. An image and event sequence reconstruction video databases of both firearms and replicas were created in order to better define firearm-specific functional morphological features. We demonstrate that it is possible to classify an object as a firearm by analyzing the functional, and not only the esthetic, morphology in images and video. It is also shown that event sequence reconstruction in video may be used to infer that an object suspected as a firearm has the capacity to shoot by confirming the occurrence of a shooting act or shooting process. Thus, photographic content analysis may be used to forensically establish that an object depicted in an image or a video is a firearm by ruling out other known scenarios, and without physically seizing it.

Photographic comparison of surface topography as a viable solution when physical match is challenging.

Physical matching methods are a family of well-known methods that are utilized in order to determine whether two pieces of a tearable/breakable material used to be one object. When performing physical match of polymers, it is sometimes difficult to reach an unambiguous conclusion. This is due to various reasons. One is when the tear/fracture resides in an inaccessible or hidden-from-view region of the piece. Another is when the shape of the tear/fracture at the object's tear/fracture line is insufficient for deducing a complete match. Third is deficiency of material along this line. These are examples of processes where the line is affected so drastically, so that a match renders impossible. Specifically, when addressing elastic materials, the tear/fracture line may even be squashed. This may also be a reason for difficulty in performing a physical match. In this paper, a method is proposed where a match is alternatively achieved by means of photographic comparison of marks on the surface topography of the pieces-in-question. Comparisons of pairs of torn pieces of silicon rubber were made. The procedure involved photography of the surface topography the pieces. Then, the photographs were horizontally mirror-flipped. Lastly, a comparison was made between two photographs: a photograph of one piece and a mirror-flipped photograph of the opposite piece. The results show that after comparing the pieces to one another, only one unique pair turned out to be positively matched. Using the proposed method, not only the comparison is done by a more informative method (comparing to physical match), it is also more convenient, faster, less expensive, and technically simpler.

Friction Marks of Stabbing Tools in Tires.

When receiving a stabbed tire for examination, forensic toolmark examiners can determine whether a suspect tool was used in a specific crime based on class-characteristics and individual-characteristics marks that have been left by the tool on the tire. This study discusses friction marks and their forensic value during the examination of a punctured tire. The term friction mark refers to the noticeable mark around the penetration area on a tire's surface. Tires designed to create high friction when contacting a road. Due to this design, friction is created between the stabbing tool shank and the sides of the hole. As a result of this friction, the shank of the stabbing tool wears the outer layer of tire around the hole. This leaves a friction mark whose general shape reflects the cross-sectional shape of the stabbing tool's shank. This phenomenon was observed and named by Locke (7) in his evaluation of tire puncture marks with knives. This article demonstrates the same phenomenon with other types of stabbing tools. Test stabs were produced with different tools representing a variety of cross-sectional shapes of shanks, and the resulting friction marks were photo-documented and discussed. Correlations between the various cross-sectional shapes and their corresponding friction marks are shown. Based on friction mark examination, the examiner: (i) can infer suspect tool shank cross-sectional shape with the evaluation of the friction mark shape and (ii) can deduce the maximum dimensions of the shank. This examination simplifies and accelerates the forensic comparison procedure and the investigation time.

Photographic Image Comparison of Vegetation.

Images and videos are common types of evidence in crime scene investigations and laboratory analysis. Images may be taken by the suspect and/or by crime scene investigators and may serve as crucial elements in forensic laboratory analysis. Forensic photographic image comparison is the process of comparing one or more objects or persons in photographs/images when at least one image is known to be related to a crime. The forensic examiner usually compares the images in order to determine whether or not an association between the exhibits in the images can be made. This paper proposes an extension to the currently prevalent photographic image examination method. The extension introduces comparison of landscape and vegetation over time. It is revealed that similarities between images may still be found between the period of time the suspect photograph was taken and the period the crime scene investigator took the photograph from the same area. In this case report, two suspects to be involved in growing a marijuana field were arrested by the police. The forensic experts were asked to examine images taken by the crime scene investigators and to compare them to the images found in the suspects' phones. They then tried to determine whether the suspects could be linked to the specific locations. While applying techniques derived from morphological comparison methodologies, the plants at the scene provided significant additional information. A tree trunk, branches, and twigs on a hedge in the photographs revealed specific individual characteristics that led the examiner to reach a conclusive decision.

Using headlight patterns in vehicle recognition.

Crime scenes are frequently poorly lit, making it difficult to recognize and identify implicated vehicles that have been caught on film or photographed during incidents. This paper explores vehicle recognition capabilities in dark images, specifically as when a vehicle's headlights are on and are projecting light onto a flat vertical surface. In this study, the headlight reflection patterns of 68 vehicles were photographed and analyzed. This paper presents a method for confirming or ruling out a vehicle's make and model by its headlight pattern.

A new method for opening quartz halogen light bulbs in vehicle accident investigations.

After a car accident, it is an important forensic task to evaluate the status of the vehicle's lighting at the time of impact. In some cases, the bulb has to be opened up to allow proper examination of the high and low beam filaments. Quartz halogen pressurized bulbs are both rigid and brittle and their internal pressure makes them likelier to explode. This study aimed to develop a more elegant method of breaking halogen bulbs open that would minimize the danger of explosion and the risk of damaging the filaments in the process. As part of the study, several opening methods were tried on multiple pressurized quartz halogen bulbs, such as cutting a groove with a hacksaw or a rotary tool, using a propane torch on the bulb to cut or warm it and then cooling it rapidly. Repeated testing by several examiners has shown that the new method developed in this study is the safest and easiest compared with other established methods.

Effect of Cutting with an Abrasive Saw on Swarf Composition.

Crime scene investigators are often asked to examine swarf from break-in sites and compare it with swarf found on a suspect. Occasionally, elemental composition of swarf from these two sources does not match. It is generally assumed that cutting metal does not induce changes in chemical composition. However, this study shows that, if a matrix contains iron, chromium, and nickel, composition of swarf produced from cutting the matrix with an abrasive saw may indeed alter. In this study, we cut a stainless steel sheet using a standard cutoff saw. Swarf was sorted and chemically analyzed by EDS/SEM, and the following relationships between chip morphology and modified composition were discovered: elongated chips remained unchanged; changes in the irregular chips appeared to be random, possibly because they are formed in a number of different ways; composition of spherical chips changed with size.

Improve Toolmarks' Impressions in Soft Wax.

When the forensic toolmarks laboratory receives for examination and comparison a tool that is suspected of having been involved in a crime, the expert performs tests designed to determine whether or not the specific tool generates the same toolmarks as those found at the crime scene. This is performed by testing tool striation on a piece of soft metal, such as lead, and examining the marks left by the tool. Studies have shown that wax may be an optimal material for this purpose. This study examines the use of wax at different temperatures and shows that quality of results is better when the wax is cooled (recommended temperature is -18°C). At this temperature, the wax is flexible enough but does not smear and is not sticky. This makes the obtained marks clearer and of better quality.

Toolmarks made by lathe chuck jaws.

This paper presents a forensic method to evidentially tie a workpiece with a specific lathe. Examining using this method can prove or exclude a connection between the two. The importance of this method is mostly due to the growing trend among lawbreakers of manufacturing improvised firearm parts using machining processes. This method is based on comparing jaw impressions made by the chuck on a workpiece.

Bolt Cutter Blade's Imprint in Toolmarks Examination.

Bolt cutters are known as cutting tools which are used for cutting hard objects and materials, such as padlocks and bars. Bolt cutter blades leave their imprint on the cut objects. When receiving a cut object from a crime scene, forensic toolmarks examiners can determine whether the suspected cutting tool was used in a specific crime or not based on class characteristic marks and individual marks that the bolt cutter blades leave on the cut object. The paper presents preliminary results of a study on ten bolt cutters and suggests a quick preliminary examination-the comparison between the blade thickness and the width of the imprint left by the tool on the cut object. Based on the comparison result, if there is not a match, the examiner can eliminate the feasibility of the use of the suspected cutting tool in a specific crime. This examination simplifies and accelerates the comparison procedure.

A physical match of a metallic chip found on a bolt cutters' blade.

Bolt cutters are known as devices which are used for cutting hard objects and rigid materials such as padlocks and bars. They are commonly used in instances of forced entries. In this case study, a bolt cutter was found in the car of two suspects in a grocery burglary. This study indicates how the presence of a small metallic chip found on a suspected bolt cutter can prove that the tool was used in the crime scene. During the initial examination, a metallic chip from the cut shackle padlock was found stuck to one of the bolt cutters' blades. By comparing the metallic chip's microscopic edge and the breaking (fracture) line of the padlock's shackle, a full physical match was noticed. We wish to report here how residue, even the smallest, can be used to link burglary tools to a crime scene with a high level of certainty.

The class characteristic mark of the H&M Mul-T-Lock picking tool in toolmarks examination.

Mul-T-Lock is a high security lock cylinder distinguished by the use of a telescoping "pin-in-pin"-tumbler design. Picking the Mul-T-Lock cylinder with a traditional picking tool is highly complicated because it can get stuck between the inner and outer pins. The H&M Mul-T-Lock picking tool was designed to overcome this problem and facilitate the picking of the "pin-in-pin" cylinder. The purpose of this research is to determine whether H&M Mul-T-Lock picking tool leaves class characteristic mark and whether it can be distinguished from traditional picking tools marks and from regular key marks. It also describes and determines the class characteristic mark left on telescopic pins, its origin, recurrence, and its benefit to the toolmarks examiner. When receiving a Mul-T-Lock from a crime scene, a toolmarks examiner can quickly determine whether or not it was picked by an H&M Mul-T-Lock picking tool by noticing the class characteristic mark which this typical tool leaves.