Importance of Cartridge Case in the Criminal Investigation

The criminal investigation is an applied science that pertains to the study of facts that are then used to inform criminal prosecutions. A complete criminal investigation searching,  interviews,  interrogations,  evidence collection and conservation, and numerous techniques of investigation. Modern-day criminal investigations normally assign many modern scientific methods known collectively as forensic science. And in such an investigation there is a need for the proper and detailed investigation which can be done by cartridges which help in taking fingerprints or any additional evidence. Criminal investigators collect facts and examine evidence of crimes committed at local, state, and federal levels. The United States FDA Investigations Operations Manual reports that the objective of the criminal investigation is to obtain evidence, document the facts, and report the results for a possible trial. In order to conduct a beneficial criminal investigation, you must know the basic actions of the investigative process. While types of criminal cases may vary, the following methods can be pursued to help the trial prove the case beyond an adequate doubt.


Ever wondered what a host of information a bullet can provide to forensic investigators involved in a criminal investigation? This has been made feasible by a department 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 weapons. It is particularly favorable to bullets, rockets, and unguided bombs. Simply put, ballistics is the application of science to examine the way of a bullet from a basis 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.

Ballistic Fingerprinting – The Science of Firearm Ballistics

Ballistic or cartridge fingerprinting pertains to the examination of tool mark evidence, firearm, and bullet. This helps to conform to a bullet with the firearm it was fired with. Ballistic fingerprinting is based on the fundamental principle that there are unavoidable deviations on all firearms. These are marks created during the machining process and also from normal wear and tear.

Accordingly, every firearm generates a unique imprint on the shell casing it fires. This results in a bullet necessarily leaving a different pattern on anything it hits. Ballistic experts are helpful at verifying the type of firearm used in a crime by studying the marks left on a bullet or the effect left by it on a surface. They can even remove an obliterated serial number of the weapon to trace its registered owner.

The study of firearm ballistics and firearms is often considerably divided into three categories – internal, external, and terminal. Internal ballistics is all about the procedures 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 basis to target. And, fatal ballistics also called impact ballistics, is the study of the impact of the projectile on the target.

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

Amazing Ways of Linking a Gun to a Crime Scene

Although guns and bullets are associated with the most severe and deadly crimes, they also tend to leave behind the most positive evidence. The important clues sought by crime scene investigators include bullet compartments, 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 the case of bullets entrenched in furniture or soft plaster, the portion around and including the bullet is carefully eliminated. This assures that the channel made by the bullet is conserved for further study by forensic experts.

1. Patterns left by Gunpowder Residues

Though it may seem that the bullet is the only subject that evacuates the barrel when a gun is fired. In reality, firing also expels gunpowder residues that create a different pattern on an object close to the container. 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 estimated distance from which the special firearm was used. There have been several past cases when the criminal tactfully left the victim in a state apparently suggesting a suicide. However, the absence of powder marks on the hand holding a gun or the area around a bullet hole makes the opportunities of a suicide highly unlikely.

2. Analyzing Trajectory, Bullet Cavities, and Ricochet

Tracking the flight path of a bullet considerably helps investigators copy the events of a crime. The trajectory of a bullet helps forensic ballistic experts determine the direction from which a weapon 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 former method involved the insertion of sticks and cords into the bullet holes to establish the bullet’s escape path and also the shooter’s position, height, and many other details. The newer method implicates the use of a laser to ascertain the bullet’s trajectory. Additionally, investigators can collect more details from the evidence that bullets that dart collect.

3. The 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 pellet is released. Just so you know, the primer is the volatile cap that is accountable for provoking the gunpowder when it is hit by the firing pin. Similarly, when the firing pin strikes the central ring of the cartridge case, it leaves a standard incision on it. This opinion being unique to the firing pin of a special gun can actually be used to link cartridges to specific firearms, just like the comparison of rifling marks with bullet striations. Besides, the extracting pin and the ejector inside a firearm that is responsible for ejecting the spent shell casing from the gun’s chamber also create different opinions on the shell casing which are unique to a particular firearm.

4. Tissue Damage due to the Bullet

Forensic examiners are quite qualified at uncovering an abundance of evidence from the wound inflicted on the victim. Irrespective of whether the bullet fragment is recovered or not, the wound itself can indicate the bullet type, sequence of hits, distance from which the bullet was fired, its momentum, and much more! The distance, velocity, and direction of the shot can be determined from the cracked lines in thick bones such as skulls. In fact, skimming 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 scars and bone/tissue damage opens up a whole world of data for forensic investigators.

5. Fingerprints

It is but apparent 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 caressed. The intense heat that is produced when a bullet is fired outcomes in the evaporation of the moisture in the sweat, leaving behind the salts on the surface of the gun. This is the precursor to regaining the fingerprints from its surface. Once the recovered firearm is endangered to superglue (cyanoacrylate) fumes, the gases adhere to these salts and etch the fingerprints onto the gun’s ground. The contrast of the fingerprints is further enhanced by using a fingerprint powder. Once the fingerprints are recovered, they can be fitted against a fingerprint database such as the Integrated Automated Fingerprint Identification System (IAFIS) to lead to the suspect.

6. Thorough Firearm Examination

Some suspects of shooting feign the combustion of the firearm as an accident or the finding of a weapon malfunction. A careful examination of the firearm helps establish this claim, particularly trigger pressure – the force compelled to grab a trigger. Certain guns have light trigger pulls which may result in an unexpected firing. Therefore, computing the trigger pressure can actually help infer the likelihood of an accidental discharge. Also, 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 blasting was unexpected, the firearm is subjected to a jarring test. This pertains to subjecting it to a series of effects pertaining to various distances and surfaces to consider the possibilities of an accidental explosion. Sometimes, a test-firing into water or gelatine may also be compelled in order to obtain test bullets and shell containers. This helps in fitting them with the recovered information.


Q1. Why is the cartridge case is important in the investigation?

When the firing pin strikes the cartridge case, a characteristic indentation is caused that can be used to link cartridges to a specific firearm.

Q2. How are cartridges and bullets are examined by the examiner?

It relies on unique tools marks left by various parts of the weapon including the firing pin. These marks are compared and examined by the examiner to examine fire the weapon using the same parts.

Q3. How are cartridges cases are compared?

They are compared to fired standards from a firearm using a comparison microscope as described on the bullet identification page.

Q4. What components will cause the cartridge to be marked?

Cartridge, which includes primer powder, gun powder, bullet and casing material that holds them all together.



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