Forensic Ballistics

Forensic Ballistics – Reconstructing a Crime using Bullets

Ever wondered what a host of information a bullet can provide to forensic investigators involved in a criminal investigation? This has been made possible by a branch of forensic science called Ballistics. Forensic ballistics or ballistic fingerprinting as such is a field of mechanics that is applicable to the launching, behavior, flight, and effect of projectiles. It is particularly applicable to bullets, rockets, and unguided bombs. Simply put, ballistics is the application of science to inspect the path of a bullet from source to target.

In forensics, ballistics is the science which helps deduce information admissible in the court of law or any other part of the legal system that is pertaining to the use of bullets in a crime. This is possible by the scientific analysis of bullets and bullet impacts to arrive at logical inferences about the incident. In layman’s language, forensic ballistics involves the matching of recovered bullets and their casings to the firearm from which they are likely to have been fired.

So what are the vital information that a ballistics specialist can draw from a bullet or even a bullet impression? For instance, a forensic ballistics expert can precisely determine the distance, angle and even the time when a gun was fired by carefully analyzing the damage that the bullet suffers upon hitting a rigid surface. Additionally, forensic ballistics has the potential to assist investigators in ascertaining the identity of the shooter. One way of achieving this is by examining any residue on the bullet and comparing it with that found on the suspect’s hand or body, the firearm used or any other object recovered from the crime site.

Ballistic Fingerprinting – The Science of Firearm Ballistics

Ballistic fingerprinting involves the analysis of tool mark evidence, firearm, and ammunition. This helps to match a bullet with the firearm it was fired with. Ballistic fingerprinting is based on the fundamental principle that there are inevitable variations on all firearms. These are marks created during the machining process and also from normal wear and tear.

Therefore, every firearm produces a unique imprint on the shell casing it fires. This results in a bullet inevitably leaving a distinct pattern on anything it hits. Ballistic experts are adept at ascertaining the type of firearm used in a crime by studying the marks left on a bullet or the impact left by it on a surface. They can even extract an obliterated serial number of the weapon to trace its registered owner.

The study of firearm ballistics and firearms is often broadly divided into three categories – internal, external and terminal. Internal ballistics is all about the processes inside a firearm, and the microseconds between the action of pulling the trigger and the bullet exiting the gun’s muzzle. External ballistics deals with the path of the bullet from the source to target. And, terminal ballistics also called impact ballistics, is the study of the impact of the projectile on the target.

Ballistic details gathered globally are entered into a large database accessible by worldwide law enforcement agencies. This helps investigators locate relevant data from past records/ investigations to track down a suspect.

Remarkable ways of linking a Gun to a Crime Scene

Although guns and bullets are associated with the most serious and deadly crimes, they also tend to leave behind the most explicit evidence. The crucial clues sought by crime scene investigators include bullet cavities, shell casings, blood spatter patterns and even dropped weapon(s). Once the crime scene has been photographed, diagrammed and all evidence listed, the bullet casings, bullet fragments and other significant evidence are gathered, preserved and transferred to forensic labs for study. In case of bullets embedded in furniture or soft plaster, the portion around and containing the bullet is carefully removed. This ensures that the channel made by the bullet is preserved for further study by forensic experts.

Wondering how forensic ballistics can be used to recreate a crime scene or investigate a criminal incidence? Here’s how.

1. Patterns left by Gunpowder Residues

Though it may seem that the bullet is the only object that leaves the barrel when a gun is fired. In reality, firing also ejects gunpowder residues that create a unique pattern on an object close to the barrel. The nature of the pattern varies as per the distance between the weapon and the target. Forensic ballistic experts can co-relate such patterns to the approximate distance from which the particular firearm was used. There have been numerous past cases when the criminal(s) tactfully left the victim in a state ostensibly suggesting a suicide. However, the absence of powder marks on the hand holding a gun or the area around a bullet hole makes the chances of a suicide highly unlikely.

2. Analyzing Trajectory, Bullet Cavities, and Ricochet

Tracing the flight path of a bullet significantly helps investigators recreate the events of a crime. The trajectory of a bullet helps forensic ballistic experts deduce the direction from which a projectile is fired. Once bullet holes are located on floors, walls, ceilings or other places/objects at the crime scene, investigators can use two methods for determining the trajectory. The older method involved the insertion of sticks and strings into the bullet holes to establish the bullet’s flight path and also the shooter’s position, height, and many other details. The newer method involves the use of a laser to ascertain the bullet’s trajectory. Additionally, investigators can gather more details from the trace evidence that bullets that ricochet collect.

3. Striations on a Fired Bullet

What makes every firearm unique is the process of ‘rifling’ that during the manufacturing of its barrel. This process results in the creation of a series of grooves and spirals along the inside of its barrel. These grooves are necessary as they provide the requisite spin to a bullet in order to improve its flight accuracy and stability. Therefore, a bullet once fired always bears markings that mirror the spiraling grooves and lands inside the firearm barrel. This is a crucial evidence to match a bullet to the weapon used for firing it as no two grooves within a firearm barrel is the same, just like fingerprints!

To further narrow down to the specific firearm used, ballistic fingerprinting experts analyze and measure the type, angle, and the number of the spiral grooves, and also inspect if they rotate anti-clockwise or clockwise. However, use of shotguns in a crime is likely to leave forensic investigators scratching their heads to trace it back. This is because such guns lack rifling due to which the bullets shot from them do not have any striations.

4. Firing pin, Extractor pin, and Ejector Impressions

When a gun is fired, the firing pin strikes the center of the cartridge to ignite the primer and it is only then that the bullet is released. Just so you know, the primer is the explosive cap that is responsible for igniting the gunpowder when it is hit by the firing pin. Furthermore, when the firing pin strikes the central ring of the cartridge case, it leaves a characteristic indentation on it. This impression being unique to the firing pin of a particular gun can actually be used to link cartridges to specific firearms, just like the comparison of rifling marks with bullet striations. Additionally, the extracting pin and the ejector inside a firearm which are responsible for ejecting the spent shell casing from the gun’s chamber also create distinct impressions on the shell casing which are unique to a particular firearm.

5. Tissue damage due to the bullet

Forensic examiners are quite skilled at uncovering a plethora of information from the wound(s) inflicted on the victim. Irrespective of whether the bullet fragment is recovered or not, the wound itself can reveal the bullet type, sequence of hits, distance from which the bullet was fired, its velocity and much more! The distance, velocity, and direction of the shot can be determined from the cracked lines in dense bones such as skulls. In fact, grazing bullets are known to create little areas of ragged skin that are hauled up and torn due to a high-speed bullet. Therefore, the nature of wounds and bone/tissue damage open up a whole world of information for forensic investigators.

6. Fingerprints

It is but obvious that a gunman would be physically handling the bullets while loading them into a cylinder. This results in the deposition of sweat on the surface of the firearm every time it is touched. The intense heat that is generated when a bullet is fired results in the evaporation of the moisture in the sweat, leaving behind the salts on the surface of the gun. This is the precursor to recovering the fingerprints from its surface! Once the recovered firearm is exposed to superglue (cyanoacrylate) fumes, the fumes adhere to these salts and etch the fingerprints onto the gun’s surface. The contrast of the fingerprints is further improved by using a fingerprint powder. Once the fingerprints are recovered, they can be matched against a fingerprint database such as the Integrated Automated Fingerprint Identification System (IAFIS) to lead to the suspect.

7. Extraction of Serial Number

Every legally produced firearm is etched with a unique serial number during its manufacturing. The engraving process results in the impressing of the digits below the surface of the metal too. Often a criminal uses his devious ingenuity to destroy this serial number by filing/grinding to avoid tracing the weapon. However, the fact that they are completely oblivious to is that these serial numbers can be recovered by forensic scientists. Two commonly used techniques for the same are – Chemical restoration and magnetic particle inspection. Various reagents are available for restoring the serial number by the reacting them with the surface of the firearm. However, chemical restoration often ends up damaging the evidence to a great extent and is usually the last resort when magnetic inspection fails. Once the serial number is successfully recovered, it helps determine the weapon’s history as well as its owner.

8. Thorough Firearm Examination

A thorough examination of a firearm helps deduce whether it was actually used for firing the shots in question or not? Although a number of evidence recovered from the incident scene (cartridge cases, spent ammunition, gunshot residues, wounds etc.) can be used to establish this, firearm examination is also as much crucial in ascertaining its link to the crime.

Some suspects of shooting feign the discharge of the firearm as an accident or the result of a weapon malfunction. A careful examination of the firearm helps establish this claim, especially trigger pressure – the force required to pull a trigger. Certain firearms have light trigger pulls which may result in an accidental firing. Therefore, calculating the trigger pressure can actually help determine the possibility of an accidental discharge. Additionally, it is also essential to verify if the firearm had an option of selecting a normal trigger pull or a light trigger pull. In order to determine if the firing was accidental, the firearm is subjected to a jarring test. This involves subjecting it to a series of impacts involving various distance and surfaces to consider the possibilities of an accidental discharge. Sometimes, a test-firing into water or gelatin may also be required in order to obtain test bullets and shell casings. This helps in matching them with the recovered evidence.

Incognito Forensic Foundation (IFF Lab) – A premier private Forensic Lab in the league of criminal investigations

Incognito Forensic Foundation (IFF Lab) is a premier private forensic lab headquartered in Chennai and with an office in Bangalore. Having a repertoire of forensic experts handpicked from premier forensic institutes, it strives to stay a step ahead of the rest. IFF Lab has a state-of-the-art forensic laboratory and adopts the latest tools and techniques in conducting criminal investigations. They have assisted law enforcement agencies across India in the investigation of complex and highly sensitive cases. Apart from criminal investigations, they have also emerged as the pioneers in cyber and digital forensics. A valuable addition to the forensic domain, IFF Lab stands by its commitment to provide selfless service to the nation.

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