Details in the Bullet
The Role of Firearms and Ballistics in Forensic Investigations
What is forensic firearm investigation?
Forensic firearm examination is all about studying firearms, ammunition, and other pertinent forms of evidence present at crime scenes.
This branch of forensic science covers a wide range of applications and is integral in solving criminal cases involving firearms.
Firearms & Ammunition
What are they?
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A firearm is a gun that uses a controlled explosive charge to propel a projectile from its barrel.
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The projectile comes in the form of ammunition.
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A round of ammunition consists of a bullet that is expelled from the firearm and a metal casing that is separated from the bullet.
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When the shooter pulls the trigger, the firing pin hits the primer, a small metal cup that contains explosive chemicals inside it.
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Chemicals in the primer ignite the gunpowder stored in the casing, causing the explosive charge that propels the bullet.
What is forensic ballistics?
Ballistics is the area of physics that studies projectiles during their motion and impact.
In forensic cases involving firearms, this concerns the study of four aspects of a bullet’s motion during shooting.
Internal Ballistics: Detonation of the bullet and its expulsion from the barrel.
External Ballistics: Changes in velocity and trajectory as the bullet moves through the air.
Transition Ballistics: Impact of forces like air pressure and gravity on the bullet as it exits the barrel.
Terminal Ballistics: Impact of the bullet on the object it contacts.
These phases of a bullet's travel path are typically examined by a Forensic Ballistics Expert to determine information such as the location of the shooter at a crime scene and the trajectory of the bullet.
Ballistic Links
Ballistic links are one of several forms of evidence that can be obtained from crime scenes involving firearms.
Serial Numbers
A chemically restored serial number on the body of a firearm.
Every firearm has a unique serial number on it that can be used to trace the purchase and ownership of a specific firearm through official databases.
This is important in identifying the owner of a firearm, but some criminals file the serial number off the firearm to make it seemingly untraceable.
There are methods available to forensic scientists to restore obliterated serial numbers.
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The process of imprinting the serial number onto the firearm during manufacturing alters the metallic structure in the location where it’s set.
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A forensic scientist can add a chemical etchant to the metal where it has been filed off.
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The altered metal reacts differently to the etchant than the surrounding metal and reveals the imprint pattern of the serial number in its original location.
Gunshot Residue
Gunshot residue (GSR) is among the most useful kinds of evidence available at firearm crime scenes - so what is it exactly?
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A heterogenous cloud of particles composed of the burned propellant that is discharged from a firearm’s barrel when bullets are fired.
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The presence of GSR at a crime scene is particularly useful if no bullets or casings were found at the scene - GSR is another indicator a firearm was discharged.
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Can also provide intelligence of firing distances as well as entrance and exit wounds made by bullets.
GSR will often be discharged from a firearm onto the shooter in trace amounts, and so clothes from a suspect can be examined for the presence of GSR.
Forensic scientists use tape lifts and adhesive stubs to recover GSR from surfaces for analysis. The composition of GSR has many components but prominently include trace amounts of lead, barium, and antimony. Forensic scientists perform tests to identify these metals when seeking to confirm the presence of GSR.
Analysing Gunshot Residue
A sodium rhodizonate colour test can be done to screen for the presence of lead, a strong indicator that GSR is present. A colour change in the presumed GSR sample to dark red or pink is expected and would indicate that lead is present. This is a common screening test for GSR that would be performed before analytical techniques are applied.
Example of a sodium rhodozinate test to screen for the presence of lead on clothing.
A more analytical approach to examining GSR involves SEM-EDX, which utilises scanning electron microscopy and energy dispersive x-ray spectroscopy. This technique allows forensic scientists to study the elemental composition and particle morphology of a sample of particles recovered from the crime scene. If the expected metals of GSR composition are present and the morphological shape of the particles is correct, forensic scientists can positively confirm that GSR is present in a sample. This is critical in evaluating crime scenes and supporting claims such as the discharge of firearms or firing distance determination.
GSR particle imaging with SEM and elemental analysis of GSR with EDX.
How has forensic ballistics been used in real criminal cases?
The Oscar Pistorius Case
In 2013, professional athlete Oscar Pistorius killed his girlfriend, Reeva Steenkamp, by shooting her through a bathroom door in his house. The forensic analysis of this case focused on:
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Analysing the bullet trajectory to determine Pistorius’ location when shooting.
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Examining the entry and exit wounds on Steenkamp in comparison to the bullet trajectory to determine her location when she was shot.
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Comparing the wounds to the bullet holes in the bathroom door to correlate impact angles.
These aspects of the case were vital in reconstructing the incident, leading to the eventual conviction of murder. Pistorius was sentenced to 13 years of imprisonment in 2017 and released on parole in 2024.
Further Reading
For more comprehensive reading on ballistics as an area of forensic science, click here.