expert testimony

Image credit: Security Magazine

This extra session is intended to show you yet another technique that you can add to your forensics projects. In fact, firearms are one of the most common tools used to commit a crime. The contents displayed here range from basic knowledge about weapons and projectiles to advanced techniques such as calculating trajectories and analysing gunshot residue in the laboratory, as well as computer-based recreation of famous crimes. I hope you learn a thing or two.

NOTE: There is no iDoceo activity associated to this session. Answers are included here, so you do not have to submit anything on ballistics.


- Contents

  1. The basics
    1. Cartridge components
    2. How does a bullet work?
    3. Parts of a gun
  2. Bullet trajectory
    1. How to determine trajectory
  3. Gunshot Residue Analysis
    1. Processing GSR in the lab
  4. The 'magic bullet'
    • JFK's assassination
    • JFK's assassination computer recreation

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Cartridge components
Cartridge components
Image credit: Bulk Munitions

Hollywood has contributed greatly to our extensive expertise (at least in fiction) in different types of weapons, ammunition (a.k.a.'ammo') and things that go "bang" in general. But, how much do we really know about the basics of physics and mechanics in gun shooting? How does a bullet actually work?

The first thing we need to know is that what we call a bullet is in fact called a cartridge, and the bullet is only part of the cartridge.

Learn the different components of a cartridge in the following exercise.

Cartridge components

Use the labels in the image below to fill in the missing words in the following description of a cartridge.

Cartridge components
Cartridge components
Image credit: A Girl & A Gun

Although the word bullet is often used in colloquial language to refer to a cartridge round, a bullet is not a cartridge but rather a component of one.

A round of ammunition cartridge is a combination package of the (1) (which is the projectile), the (2) (which holds everything together), the propellant or (3) (which provides the majority of the energy to launch the projectile) and the (4) (which ignites the propellant).

A shotgun cartridge (5) is made from plastic or fibre. Plastic wads usually have “petals” that expand to create a seal within the bore of the barrel, whereas fibre wads have to be compressed when they are placed in the case.

A (6) cartridge is a metallic cartridge whose primer is located at the center of the base of its casing, whereas (7) ammunition is a type of firearm metallic cartridge whose primer is located within a hollow circumferential rim protruding from the base of its casing.

Check answers

How does a bullet work?

Watch this video and progress from beginner to expert in just 30 seconds.

Parts of a gun

Now have a look at the following diagram. Do you know the names of the different parts of this gun? When you are sure you have all your answers ready, take the following challenge.

expert testimony

The gun in the image is a Glock 19.


Parts of a gun. Choose the correct answers and beat your colleagues in accuracy and speed!


How to determine bullet trajectory

Crime scene analyst Matthew Steiner teaches the techniques forensics experts use to determine bullet trajectory in a crime scene, ranging from easy to difficult. Matthew shows how forensic analysts use protractors, string, lasers and 3D laser scanners to investigate crime scenes.

Assorted vocabulary

The following words are related to shootings and explosive projectiles in general. Can you guess what they mean. Match the terms and the explanations.

azimuth - blank - caliber - point blank - recoil - ricochet - rifling - scope - shrapnel - wipe

  1. When a bullet strikes a target it may be deflected from its original path as a result of impact and travel in a direction quite different from its original one.
  2. Also known as knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged.
  3. Small pieces of metal that fly through the air when a bomb or similar weapon explodes and are intended to injure people
  4. A shot, bullet, or other missile fired from very close to its target.
  5. The width of the inside of the long, cylindrical part of a gun, or the width of a bullet.
  6. A gray or black ring around an entrance bullet hole. The ring is formed by and contains bullet lubricant, byproducts of propellant, traces of bullet metal, and residue in the gun barrel from previous use.
  7. The angle of a bullet hole, from left to right or from right to left.
  8. More technically known as a telescopic sight, it is an optical device based on a refracting telescope.
  9. Firearm cartridge that generates a muzzle flash and an explosive sound like any normal gunshots, but without shooting a projectile
  10. Marks left on the bullet as it spins inside the gun barrel when being shot.

Check answers


Processing GSR in the lab

Forensic investigations often rely on the evidence of gunshot and other firearms-related residues. When one fires a gun, the explosion creates a fine cloud of particles. These particles consist of burnt and unburnt powder, as well as traces from the bullet, its casing, and the gun itself. As the cloud settles, it lightly coats the area with gunshot residue (GSR). GSR will likely cling to the shooters hands, exposed skin, and clothing. Investigators usually sample this evidence with GSR test kit stubs. They can often obtain even more evidence from bullet-wipe deposits, partially burnt or unburnt powder, and trace materials on the bullet.


John Fitzgerald Kennedy’s assassination
JFK in Dallas

JFK in Dallas right before his assassination
Image credit:


1. What do you know about the 1963 JFK assassination? Why is it so controversial even today?

2. What is the Single-Bullet Theory?

JFL assassination computer recreation

Watch this short video explaining that one single bullet could have killed JFK and injured Governor Connally. What do you think?

JFK in Dallas
Among the flood of conspiracy theories that have risen and fallen in the years since the 1963 assassination of President John F. Kennedy, one theory has remained the focus of intense debate: the single-bullet theory.

This theory, supported by the 1964 findings of the Warren Commission investigating Kennedy's assassination, posits that the president was shot by the same bullet that also injured Texas Gov. John Connally, who sat in the front seat of the presidential limousine. Some critics sarcastically refer to this as the "magic-bullet theory."

The trajectory of the bullet that supposedly penetrated Kennedy's neck and Connally's torso is one of the many points of contention of the single-bullet theory. Critics charge that because of the position of the two men in the limousine, the bullet would have had to change course in midair to travel as proposed.

The fact that Connally was seen holding his hat in his right hand also caused suspicion, since he was supposedly wounded in his right wrist by the single bullet. The unusual circumstances surrounding the discovery of the CE 399 bullet —it was reportedly picked up off the floor by a nurse, or discovered by a hospital engineer, according to various reports— and the bullet's so-called "pristine" condition, have also given conspiracy theorists a lot to say.

The single-bullet theory gives credibility to the conclusion of the Warren Commission and other research that Oswald acted as a lone gunman who shot Kennedy because of Oswald's pro-Communist leanings and/or because of his depressed mental state.

Whether Oswald was a lone gunman, or was a pawn of Communist Cuba, or the Soviet Union, or the Mafia, or some other group, may never be known, especially since Oswald was murdered by Dallas nightclub owner Jack Ruby shortly after his arrest.

Marc Lallanilla,


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