Forensic Investigation of Bullet Holes for Determining Distance from Glass Fracture Analysis

Research Article

Austin J Forensic Sci Criminol. 2021; 8(1): 1085.

Forensic Investigation of Bullet Holes for Determining Distance from Glass Fracture Analysis

Butt A¹*, Ali A¹, Ahmad A², Shehzad M³ and Malik A¹

¹Institute of Molecular Biology and Biotechnology (IMBB), The University of Lahore, Lahore, Pakistan

²Firearms & Tool Marks Section, National Forensic Science Agency (NFSA), Islamabad, Pakistan

³Govt. Graduate College, Model Town Lahore, Lahore, Pakistan

*Corresponding author: Aisha Butt, Institute of Molecular Biology and Biotechnology (IMBB), The University of Lahore, Lahore, Pakistan

Received: February 26, 2021; Accepted: April 08, 2021; Published: April 15, 2021


The study of glass fracture patterns has been of long interest to the forensic community. Fragments of glass can be significant evidence found in the investigation of various types of offenses especially where armed violence is involved on automobiles. Figuring out, whether glass fragments present on crime scene share the same origin as per glass that has been hit by a projectile or any substrate, is quite a success to an examiner because that further leads to the investigation of how and by which means it has done. Holes occurred in the glass at the crime scenes have much importance and many attempts are taken to investigate the properties of these glass holes to find the type, speed, and angle of the projectile which probably produce the hole. For highvelocity projectiles including bullets, these bullet holes in glass can exhibit certain features and fractures. The objective of this research was to determine the distance of shooter from the bullet hole on glass used in automobiles. Bullet holes were prepared and different parameters of glass fractures like bullet hole diameter, cone fractures radius, cone fractures diameter, radial, and concentric fracture count were considered from both front and the backside of the glass. These parameters were observed and analyzed to determine the dependency of these parameters on the variable “distance”. The consistency found in the measurements to conclude our results were checked by goodness of fit test. The study bears great significance as it could lay down a foundation to set a standard parameter to estimate distance of bullet hole from shooter in firing incidents involving glass fracture. This will provide a blueprint to crime scene investigators in order to reconstruct the crime scene for understanding and to take investigation to logical conclusion.

Keywords: Fracture pattern analysis; Bullet hole investigation; Hole diameter; Low-velocity firearm (pistol); High-velocity firearm (rifle); Hole diameter, Laminated glass; Tempered glass


Fragments of glass are substantial physical evidence found in different kinds of scenes in an investigation. Such cases where firearms are involved, glass fractures may provide valuable information related to what happened and help in investigating the crime scene [1]. Glass can be fractured intentionally or unintentionally at the crime scenes. The forensic community has been interested in fracture pattern for long now, as analysis of glass fracture pattern known as “fractography” is very helpful to create link and sequence between events that occurred and evidence that was available on the crime scene [2]. The use of firearms especially improvised firearms and reloaded ammunition in criminal activities has been an alarming situation for law enforcement agencies. Analysis of glass fracture pattern often provides much significant information like causes of fracture, the direction of a bullet hitting the target, impact on fracture pattern from distance and direction, etc.

In criminal examinations, valuable data can be interpreted through understanding and assessment of glass cracks. Crack surfaces can be legitimately associated with the way glass objects are broken, hence revealing much information about the crime that has occurred. This relativity was credibly shown by research that has previously been conducted. Often forensic scientist has to look back further to process the applied stress with the external forces due to which fracture has been followed. Those forces include the impact of blunt objects at relatively low velocity and high velocity considering bullet impacts are mainly of forensic interest. Glass breakage is studied depending on the nature of crime scene, as other than impact forces; if crime scene involves arson case then thermal stresses may also be a reason to cause the fracture.

While analyzing the origin of fractures, Richard [3], presented crack patterns of fracture found to be in accordance with previous studies. He found first surface feature to be mirror zone that is the smooth region. After that, the rough region starts with not very defined boundary but it can be easily distinguished from smooth region known as the mist region. After the mist region, further instability leads towards the hackle region. These are the radiating lines away from the fracture origin but are not very definitive as radial cracks and can lead towards the mist region back to mirror region and origin of fracture. These regions are formed concentrically all around the impact point and can be said to appear in the fracture process as its occurrence pattern.

Md. Ansari [4] while studying the influence the influence of projectile nose shape and angled fire damage on laminated glass fiber, observed the impact caused on laminated glass that as the shape of the projectile was changed from conical to blunt the damaging impact was increased.

Much work has been done in recent years on glass fracture pattern analysis on window panes by an air rifle [2]. It was found that their high-velocity projectiles caused bullet hole, double of their calibre size while pistol projectile caused somewhat nearby size of the calibre. Whereas in case of improvised weapon, hole diameter was found in a greater number of variations.

To know the effect of change in pellet shape; a study was conducted [5] and found a consistent range in hole diameter formed due to both types of pellet shape: round nose and flattened nose. The identification of pellet shape from studying fracture pattern of hole diameter and shape of hole diameter was not possible.

Another study was done with air rifle on window panes of different thickness than in previous one to study multiple fractures [6]. Difference in hole diameter was found; it was concluded that hole diameter of first shot was larger than that of second shot in the transparent glass of 4mm, and 5mm thickness. Whereas in the type; privacy glass of 4mm thickness the hole diameter of second shot was larger than the hole diameter of first shot. These point are said to be indicative for the study of multiple fractures.

A research [7] was carried out to study effect of high velocity projectile on window panes and observed the fracture pattern consistent with the prior findings. It also established that increase in distance for some meters does not change the impact that much.

With all the literature review it was observed that little work has been done for analysis of bullet holes on automobile glass for determining distance. For this purpose this research has been a novel and pioneer step in forensic science regarding the reconstruction of crime scene. This research is focused on the bullet hole investigation for determining distance of the shooter from target on the glass that are used in automobiles i.e., laminated glass and tempered glass. When automobiles are present as primary or secondary evidence in crime scenes where firearms were involved, most likely glass pieces are present as evidence inside the automobile and outside as well. Glass pieces can be caused due to some accidental breakage or in case of firearms involvement; these pieces can be of bullet holes present in the glass. Bullet hole and its impact vary according to the target; in case where target is glass, bullet hole and its fractures give a pattern. This pattern contains similar type of features like bullet hole shape, cone fractures, radial & concentric fractures; by analyzing these features different parameters can be calculated about the crime. To evaluate the dependency of bullet hole and its fractures pattern on distance, this research was conducted. Firearms and its ammunition that are frequently used in shooting cases in Pakistan are considered in this research.

The analysis had done by studying the bullet hole and its features occurring on the surface and present around the bullet hole along with the three types of fracture pattern i.e., radial, concentric and cone fractures along with other surface features. When a projectile hits the glass it causes two distinct fractures, radial and concentric. Cone fractures are observed to be caused by the penetration of highvelocity projectile, such as a bullet. As Griffiths states in his fracture experiment that fractures always start from pre-existing flaws that are termed as Griffith’s flaw [6].

Parameter like change in distance also gives variety in impact pattern of bullet on glass. For this purpose bullet holes were prepared from four different distances and compared their results. To analyze bullet hole and its impact, complete glass fracture analysis was done. It was analyzed whether change in distance effect the fracture measurements or not. Change in specific interval of distance gives certain amount of difference in Measurements and these measurements were analyzed to make conclusive statement about the determination of distance with help of bullet hole analysis.

Materials and Methodology

Main focus was the analysis of bullet hole on automobile glass in this research. Automobile glass consists of two types of glass: tempered glass and laminated glass. Tempered glass is used in automobiles passenger windows and back screen (rear windshield). It is used there as safety glass because in case of any kind of accident it does not harm the passengers due to its break pattern [8].

Laminated glass; the other type used in this research is a type of glass in which plastic interlayer is a sandwich between two sheets of float glass that is done by heating in an autoclave. Thus, in event of impact; laminated glass remains intact by an interlayer, and if breakage occurs its glass pieces remain stuck to the plastic interlayer, thus protecting the passengers from injury. For this reason, automotive laminated glass is used in windshields [9].

To prepare bullet holes, four different calibre firearms that are most commonly available in crime scenes of Pakistan with their typical ammunition available in the open market were taken into account. Locally made pistols, firearms, and their ammunition are very common. .30 bore pistol (7.62x25 mm Tokarev), 9mm pistol (9x19 mm Parabellum) and AK-47 rifle (7.62x39 mm assault rifle) are the ones mostly involved in crime cases. These all firearms were semi-automatic firearms in which .30 bore pistol, 9mm pistol were of recoil mechanism where AK-47 used was of recoil firing mechanism. All ammunitions used for pistols and rifles were fully metal jacketed, centre fire, lead round and bottleneck case that consists of singlebase propellant. (Hays and Jenzen-Jones, 2018) These firearms and ammunitions shown (Figure 1) below were used to perform experimentation on automobile glass.