Patcheappan. S & Chemmalar. S
26 May 2022
“Every Contact Leaves a Trace”- Dr. Edmond Locard
Forensic Ballistics is the science of studying the effects of firearm and projectiles encountered at the crime scene. Ballistic experts or firearm examiner is a specialist who works for criminal justice system and is entrusted with the task of crime reconstruction and collecting the evidence vis-à-vis to ballistics. The opinion rendered by the ballistic expert is admissible in the court of law as per section 45 of Indian Evidence Act, 1872. The paper demystifies the concept of forensic ballistics with photographic depiction. This study examines the application and process of forensic ballistics in identifying the nature of death- whether suicidal or homicidal. The paper also examines the mechanism of firearm and wound ballistic in detail.
Key words
Ballistics, Expert, Firearms, Criminal Investigation, Wounds
1. INTRODUCTION
Exchange principle of Dr. Edmond Locard postulates that “contact between two objects result in exchange of physical materials”[1]. Analogically, when a perpetrator commits a crime, generally leaves a trace as well as take something from the scene while leaving. As a forensic expert, Dr. Edmond Locard used this principle for his criminal investigation till his death. Modern forensics refer to this principle as ‘trace evidence’[2]. This principle has its relevance in the field of forensic ballistics. Hair, fingerprint, DNA and gunshot residues are some of the examples of trace evidence transferred between the suspect and the crime scene. Forensic experts, deploy this principle for crime reconstruction and link the suspect and the victim through the trace evidence[3]. For example, gunshot residues obtained crime environment or target can be identified through scientific examination by the forensic analyst as originating from particular category of gun, the angle of the projectile and distance between the target and the muzzle.
1.1. Forensic expert
Evidence provided by the forensic expert is considered as circumstantial evidence. Circumstantial evidence is interpretation drawn from scientific analysis like, finger printing, ballistics; DNA test etc. Akin to ocular evidence, circumstantial evidence is also admissible in the court of law. Circumstantial evidence has a critical role to play in the criminal justice system when ocular evidence is not sufficient. Section 45 of Indian evidence Act 1872, is the only provision that discusses about experts, competency of the expert witnesses and the admissibility of opinion provided by such experts. As per the said provision an expert is a person “who is skilled or having knowledge in foreign law, science or art, handwriting or finger impression”. Thus, ballistic expert fall under the category of science which is admissible in court of law[4].
1.2. Ballistics
Forensic ballistics is the corroboration made by the ballistic expert on the basis of material evidence collected from the crime scene and through reconstruction of sequence of events for admissibility of law. Ballistics is a science of applied mechanics which involves the analysis of guns, motion of projectiles, and other associated phenomenon. Thus, application of science of ballistics in criminal investigation is called as Forensic Ballistics. Colonel Calvin Goddard, a forensic scientist has coined the term forensic ballistics. Wound ballistics deals with the behavior and impact of bullet in the human body.
1.3. Components of Forensic Ballistics
Forensic ballistics involves following three phases - operational aspects of the firearm, the motion of projectiles from the muzzle to target and action of projective on target. To put in simply, ballistics deals with the weapon, bullet and its effect on the target. Thus, ballistics categorized into internal, external and terminal ballistics[5]. All these three phases affects the wound ballistics.
1.3.1. Internal or Proximal Ballistics:
Internal Ballistics is the study of operational mechanism of the firearm starting from the ignition of the propellant to the exit of projectile from the muzzle. The transit of bullet through the barrel and its exit from muzzle is examined in the first phase. Therefore, internal ballistics is relating to the study of structure and mechanism of firearm and its corresponding functions like propellant pressure, velocity, cartridge case ability etc.
1.3.2. External or Intermediate Ballistics:
External Ballistics is the study flight of projectile from the ejection to its target and requires a detailed knowledge of physics and advance mathematics. This phase is multifaceted and numerous factors has to be considered for the analysis, like structure of the bullet, component filled in the bullet, even gravity of earth.
1.3.3. Terminal Ballistics:
Terminal Ballistics is concerned with the study of bullet impact on the target, be it a tissue, wood or glass. This phase includes the analysis of size, weight and velocity of the bullet[6].
2. MECHANISM OF FIREARM
Knowledge on components and mechanism of gun is indispensable for proper understanding of forensic ballistics. The operational mechanism of a firearm encompasses both physics and chemistry disciplines, since it involves energy transmission from chemical energy to kinetic energy. Explosion of propellant is referred to as chemical energy and it corresponding action of ejection of bullet is termed as the kinetic energy. Notwithstanding the gun varieties, they have common parts and serve the similar purpose. Muzzle and trigger are the common component of any gun in which muzzle is the exit point of the gun and the trigger is the part that activates the firing sequence. The component and functionality of semi-automated pistol is explained to make it jargon-free. Frame, barrel and action are the three core components of a gun wherein which frame is the main structure that holds all other parts together, barrel is the bullet discharging tube of gun and the action part includes activities such as loading, unloading and firing the cartridge[7].
Magazine contains a follower and a spring that keeps the cartridges under tension once the cartridge is loaded. Magazine spring maintains pressure on the follower to push the cartridge into loading position. Slide is pulled to the rear and freed to load the first cartridge. Slide engages cartridge and feeds it into the chamber. The sear (part that controls hammer, striker and hold) engages the striker and compresses the striker spring. Pulling the trigger drops the sear and releases the striker. The striker spring sends the striker forward. The cartridge is a casing containing the bullet, the powder and the primer. When the firing pin hits the primer, chemical energy produced inside the case and causes small explosion leading to ignition of the powder. Ignited propellant burns rapidly and propels the bullet creating equal force in opposite direction and ejects the casing. The magazine cycles the next cartridge. This process is termed as recoil of blowback[8].
Caliber is the internal section of the barrel of the gun which plays a vital role in the ascertaining the type of weapon upon the examination of its impression on ejected bullet. Caliber is internal diameter of gun barrel (bore diameter of the barrel). A bullet when fired under high pressure through a hand gun having rifled barrel expands and fills the whole cross section of the barrel. Markings of lands and grooves will be quite visible in those cases where the bullet fills the whole cross section of the barrel when fired. The internal cross section includes the caliber, the dimension of land and groove impression and also the direction of the twist of grooves and the lands, whether clockwise or anticlockwise. The existence of spiral groove stabilizes the flight of a bullet and imparts the spin to the projectile while shooting. The ballistic examiner can come to inference that the bullet has discharged from particular class of firearm.
Caliber of gauge is the measurement of diameter of gun barrel in decimals of inch or millimeters. The diameter is measured between diametrically opposed lands and not grooves. Helixometer is the instrument used to determine the internal structure of the barrel. The internal cross section of barrel is depicted in figure 3.
3. FORENSIC FIREARM IDENTIFICATION EXAMINATION
Firearm Identification is a discipline mainly concerned with determining whether a bullet was fired by particular weapon. Class characteristics and Individual characteristics plays very important role in the identification of Firearm. Firearms identification is actually a form of Tool mark Identification where the firearm, because it is made of a material harder than the ammunition components, acts as a tool to leave impressed or striated marks on the various ammunition components that come into contact with the firearm. Tool marks produced on the cartridge cases will be in two basic forms. Striated action marks and impressed action marks.
Firearm identification seeks to provide answer to many questions in the context of investigation. It involves the identification and examination of firearm /cartridges abandoned or left at the crime scene. The process encompasses restoring the obliterated or erased identification number to trace the owner, examining the markings and land/groove impression on the bullet caused due to pressure at the time of ejection, recovery of fingerprints on the surface of the firearms etc. The ballistic expert could associate the bullet with the abandoned firearm and residues of cartridges. Comparison microscope is the device used to compare two materials at the same time through multiple magnifying lenses which is center eye piece of the device.
In case firearm and cartridges are not identified in the scene of crime, bullets may be retrieved either from the wound or from the crime scene. Examination of these substances could reveal the gun variety used for the offence. In firearm identification, the retrieved bullet and cartridge casing have two characteristics.
Class Characteristics: Fired bullet retrieved from the crime scene carries some markings which is referred to as class characteristics. These characteristics include clockwise spin or anti-clock wise spin in the barrel, width of barrel, number of lands and grooves etc.
Individual Characteristics: when the gun has non-identical characters due to the result of fault in the manufacturing, it is said to have individual characters. This defect in firearm is termed as fingerprinting of firearms since the markings are unique and alike fingerprinting of individual.
3.1. Gunshot Residues (GSR)
Examination of gunshot residue exposes the manner of death- whether homicidal, suicidal or accidental? GSR provides helps the forensic expert conclusive evidence. GSR can be detected from deceased clothing, on the entrance of the wound and also from the objects of the crime scene. It is pertinent to note here that FDR (Firearm discharge residue) is not synonymous with GSR. FDR is the residue consisting both propellant particles and primer residues. Usually the mixture of lead, barium and antimony are the chemical components used as propellants. Scanning Election Microscope (SEM) is the instrument used to determine the chemical composition of residues collected by the forensic expert. Prior to this technique, decimal nitrate test was prominently used.
Analysis of GSR is helps in distance determination (the distance between the muzzle of the gun and the target) using the dispersed pattern of the residue. GSR decreases with the increase in the distance between the muzzle and target. If the muzzle is close to the surface of the body, the residue discharge would be more on the entrance wound. Moreover, distance determination is authoritative evidence for pleading self-defense in the court of law.
4. WOUND BALLISTICS
Wound ballistics is “the study of interaction of wounding agents with the tissue”[9] It is projectiles effect in the target when it hits the target and transfers its energy to it. Wound ballistics is the subset of terminal ballistics and interdisciplinary in nature involving more physics components. For better understanding of the subject, simple physics involved in the wound ballistics has to be explained briefly. The common form of wound that is caused by gunshot are laceration and incises, this occurs due to the acceleration of tissue when the bullet comes into contact with the surface of the body. By calculating the kinetic energy, the depth of the wound can be determined. The speed of the bullet expelled from the muzzle of the gun determines its impact on the tissue. Kinetic Energy and Target density are two major phenomena used for forensic ballistics[10].
When the wounding agent hits the tissue cavities are formed. The two main injuries are temporary cavity and permanent cavity.
4.1. Major type of injuries:
4.1.1 Temporary cavity –
when a substance comes in contact with the human tissue, the elasticity of the tissue acts as fluid in order to absorb the substance. The elasticity does allow the wounding agent to immediately break through the tissue. The energy transferred to the tissue from the passage of bullet causes it to move and accelerate to form a temporary cavity usually larger than the permanent cavity[11]. The size of the cavity depends upon the diameter of the bullet. The mechanism involved in temporary cavity is stretch-mechanism. The kinetic energy transferred from the bullet resistance of the tissue makes some impact on the tissue before it penetrates the tissue. This damage caused to the tissue due to tension is called temporary cavity.
4.1.2 Permanent cavity –
permanent cavity is caused by actual destruction of the tissue and the cavity may be greater than the diameter of the bullet. Mechanism involved in permanent cavity is crush-mechanism[12]. The tissue is crushed by excessive pressure due to the moving bullet along the passage. The tissue is completely broken, resulting in permanent tract.
Design of the Bullet: Bullets are usually made up of soft metal like lead and either with rounded and sharp edge. Nowadays bullets are covered with jackets made of lead, zinc and nickel. This is often referred to as jacket bullets. Jacket bullets avoid the inaccuracy caused by the scratching of the bore during its transit. Earlier lubricant was used to avoid such inaccuracy. Moreover, bullets with heavy jackets have capacity to penetrate deeper and creates narrow passage. Sectional density and velocity of wounding agent are significant factors in the science of wound ballistics. Section density is the ratio of mass to the cross-sectional area, i.e. the ratio weight of the bullet to its diameter. Thus SD = M/A. thus penetrating capacity of the projectile increases with the increase in sectional density. Velocity of the wounding agent is directly related to kinetic energy.
4.2. Wound characteristics
Gunshot wound can be either penetrating or perforating[13]. When bullet enters the body and does not exit then this wound is called penetration. In contrast, if the bullet exits body or structure after completely passing through the body then it is called as perforating. The range of fire depends on distance between the muzzle and the target. The distance can be classified as contact wounds, close range and Intermediate range.
4.2.1. Contact Wound
This type of wound occurs when the muzzle is tightly held against the tissue at the time of ejection of projectile. Contact wounds are round and equal is size and muzzles imprint are visible on the target. These wounds are caused mostly in case of suicide. The close proximity of the gun to the body causes the skin to burn and split due to the hot gas. In all contact wounds soot (black powder like substance) is deposited along the wound track. The black power is the component of propellant used in the cartridge. The contact wounds may be classified into four categories - (a) hard contact- Muzzle is placed tightly and hardly on the tissue which does not allow the gases to escape and firmly deposited in the wound and turns the particular area of the skin blackish. Soot cannot be wiped out in hard contact (b) Loose contact- Muzzle is placed loosely which allows the gas to escape while shooting. The soot is deposited on the wound around the entrance which can be easily wiped out unlike hard contact wounds. (c) Angled contact - In this category of wounds gun is placed in acute angle on the tissue, i.e., muzzle is not firmly placed on the surface of the target. Wound created by this type of contact leaves irregular patterns on the target due to the escape of gas from the gap. The soot can be less noticeable (appearance of small blackened area where soot is deposited tightly) and more noticeable region (appearance of grey area where soot is distributed loosely and these deposits can be wiped easily with the bleeding of blood) (d) incomplete contact - Even though the muzzle is firmly placed on the target, gap is created due to the uneven surface of the target. The best example for this is barrel paced on the skull. These wounds will often appear in the stellate pattern. This pattern is often confused with exit wound at the time of investigation. Effects of contact wound are depicted in the figure 5.
4.2.2. Close Range or near contact wound
Near contact wound appear when muzzle of the gun is close but not in contact with skin. In close wounds, muzzle impression and splitting of wound margin cannot be seen compared to contact wounds. Abrasion colour may be obscured by soot. However, black substance can be seen but can be wiped of easily. Thus, as the range increases, the intensity of blackening decreases[14]. The close-range wound causes when the muzzle is projected within one meter from the target.
4.2.3. Intermediate range wound
Intermediate wound occur when muzzle of the gun is held away from the target. The wound caused at intermediate range produces powder tattooing on the skin as the result of powder substances expelled from the gun. Intermediate range is between 2 to 4 meters. Tattooing leaves reddish brown puncture wounds surrounding the wound entrance. Powder tattooing is an anti-mortem phenomenon and indicated that whether the person was alive or dead at the time of shooting. Power tattooing is an impact of the chemical when it reacts with skin surface. Thus, the death of the person can be ascertained with the appearance of the colour created by powder tattooing[15].
4.3. Wound Appearances
Entry and exit wound appear in different shapes like crescent, circular, stellate or irregular. The shapes vary depending upon the density of the tissue and bullet behavior. Usually the exit wounds are larger than the entry wound[16]. Differentiating exit wound from entry wound is not always simple. Most entrance wound are circular hole with abrasions on the margin produced by stretching with tearing of the tissue surface when bullet hits. This feature is most reliable to differentiate entry wound from exit wound, since exit wound lack this feature. When the bullet enters the body vertical to the surface, the margin of abrasion is symmetric. When the bullet enters on an acute angle, the margin will be elongated on the side.
Exit wounds appear as slit or irregular hole without abrasion on the margin unlike entry wound. The basic features of exit wounds are irregular edges, often everted and free from soot and powder tattooing[17]. Most exit wound has same characters irrespective of the range, i.e., contact, near or intermediate. During the forensic examination, stellate wound can be easily be mistaken for an exit wound.
5. CONCLUSION
India’s growing gun culture concerns the entire nation which is evident from the increasing gun violence across the country. Forensic ballistics requires special skill and knowledge for carrying the investigation. Advent of science and technology has led the law-enforcement to realize the technological shift and deploy new technology in their strategies. Forensic technology is shaping forensic ballistics in new dimension like virtual comparison microscope, high-speed ballistic photography, magnetic fingerprinting / automated fingerprint identifier and calculations through algorithms etc. Paradoxically, forensic analysts across the world still rely on comparison microscope. In reality, due to cost and availability factors, these technologies are inaccessible to developing countries. The need of the hour is, the state has to take initiative to deploy new technologies in the forensic ballistics application considering the growing trend of gun violence akin to foreign countries.
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Author Patcheappan. S is Assistant Public Prosecutor, Puducherry
Co-author Chemmalar. S is Research Scholar, SRM School of Law, Chennai