The range of evidence in firearms-related cases can be as small as a piece of a bullet fragment which has rifling marks or as large as hundreds of bullets and cartridge cases and numerous firearms. Even from small samples, information can be developed to indicate the type of firearm used and possibly identify the actual firearm that was used.
Other firearms evidence that could be found at a shooting scene includes shotshell wads and shot pellets; these can indicate the gauge of the shotgun. Wads and pellets can be gathered and preserved in the same manner as bullets and cartridge cases.
By examining wadding materials, the examiner may be able to determine
the gauge of the shotgun
the manufacturer or marketer
a range of possible shot sizes based on impressions in the shotshell wad
individual characteristics (in some cases)
Gunshot residues fall into two categories. The first type is gathered from the suspected shooter’s hands with a collection kit. The purpose of the examination is to determine if a person has recently handled or fired a weapon. Since it doesn’t determine which firearm was fired or when, this testing has limited value, and many laboratories have stopped performing these examinations. The second type looks for residues on items such as a victim’s clothing in an effort to determine the muzzle-to-target distance. Many times this type of evidence is not visible to the naked eye and requires microscopic examination and chemical testing to develop. The victim’s clothing must be handled with care, air dried and stored in paper containers in order to provide useful evidence.
Propellants and other gunshot residues expelled during the firing process. (Courtesy of Jack Dillon)
How the Samples are Collected
Firearms evidence can be recovered in a number of ways and areas. Firearms themselves can be recovered at shooting scenes by crime scene investigators and sent to the laboratory. Bullets, bullet fragments, cartridge cases, shotshell wadding, etc., are normally collected individually after proper documentation/photography and sent to the laboratory. Bullet evidence can also be obtained at autopsy or in an emergency room setting. In these cases the sample should be marked as a biohazard and then sent to the laboratory. Each laboratory has written procedures for packaging and submitting evidence.
Bullets/slugs that do not strike a person are often imbedded into a nearby surface such as wood/drywall. This evidence is best gathered by cutting out a section of the material and submitting it to the laboratory to allow a firearms examiner to carefully extract it. This prevents adding or destroying any markings that could be crucial to identifying or matching the suspected firearm.
A well-trained firearms examiner should perform the evaluation and comparison of this evidence. These examiners will have received extensive training on all matter of firearms and ammunition manufacturing; evidence detection, recovery, handling and examination procedures; comparison microscope equipment and procedures; courtroom testimony and legal issues; and casework.
The Association of Firearms & Tool Mark Examiners (AFTE), an international group of nearly a thousand examiners, has developed an examiner training course which takes 18 to 24 months to complete. Visit the online version of this training ▸ AFTE also offers a certification process for qualified AFTE members in three separate areas: Firearm Evidence Examination and Identification; Toolmark Evidence Examination and Identification; and Gunshot Residue Evidence Examination and Identification.
Most state crime laboratories in the US have a firearms examiner(s) on staff who can perform analysis for police departments within their jurisdiction if the need arises. Some police agencies have their own qualified examiner on staff.
How and Where the Analysis is Performed
Most examinations are performed by crime laboratory employees who are trained to conduct this type of examination. However, there are private laboratories/companies that can also perform this type of examination for a fee; often these are staffed by retired examiners. Whichever is selected, the evidence needs to be submitted for examination along with any firearms collected following the policies and procedures set down by the submitting agency.
Actual items of evidence are submitted to either crime laboratories or private laboratories according to the requesting agency’s policies and procedures. These items should be submitted in a manner that follows good chain-of-custody protocols.
The laboratory will have certain items of equipment available to conduct the examinations required. Measuring devices such as calipers and balances are used to weigh and measure bullet evidence. Stereo microscopes are used to determine basic class characteristics of fired bullets, bullet fragments and cartridge/shotshell cases. A comparison microscope is used for the examination of fired bullets, bullet fragments and cartridge/shotshell cases. Equipment used for the examination of firearms include the above items plus special equipment to measure the trigger pull of the firearm and examine the interior of the barrel. Also there must be facilities to test-fire the submitted firearm and recover fired bullets and cartridge cases. Most laboratories use a water recovery method, which is a large tank of water with a port into which the firearm is discharged. There are other systems used as well, such as metal boxes containing cotton waste material.
Examiner using a comparison microscope to analyze two .22 caliber casings. (Courtesy of NFSTC)
A comparison microscope is used for the examination of fired bullets, bullet fragments and cartridge/shotshell cases. Equipment used for the examination of firearms
examination of firearms
Forensic firearm examination is the forensic process of examining the characteristics of firearms or bullets left behind at a crime scene.
https://en.wikipedia.org › wiki › Forensic_firearm_examination
For roughly a century, forensic ballistics experts have been comparing bullets and cartridge cases by visually examining them under a split-screen microscope. After comparing the bullets, the examiner can offer an expert opinion as to whether they match but cannot express the strength of the evidence numerically.
Summary of Duties: A Firearms Examiner examines and identifies firearms, weapons, cartridges, bullets, and similar evidence in criminal investigations; collects physical evidence at crime scenes; testifies in court concerning the results of examinations; provides expert testimony on general firearms capability and ...
This is done by comparing the markings made on the cartridge cases or bullets when fired, using the firearms examiner's key tool: the comparison microscope. In conjunction with this, the examiner has the ability to explain how a firearm functions and what safety features a firearm might have.
The Firearms discipline examines and compares bullets, cartridge cases, and shotgun shells to determine if they were fired from a particular firearm. This work is part of the forensic discipline known as Firearms Identification.
Gun shot residue is tested by lifting samples off a defendant's hands or clothing and then testing to see if the lifts contain a fused particle of barium, antimony, and lead, which are known to be present in GSR.
The critical tools necessary for firearm/toolmark identification include the comparison microscope, appropriate facilities, specialized tools, equipment, instruments, and supplies. Each laboratory will also have a unique configuration of computer systems and software for technical and administrative purposes.
A comparison microscope is used for the examination of fired bullets, bullet fragments and cartridge/shotshell cases. Equipment used for the examination of firearms include the above items plus special equipment to measure the trigger pull of the firearm and examine the interior of the barrel.
How the Ballistics Database Makes Catching Criminals Easier. Studies show it can take months to a year to process gun casings in most law enforcement agencies, allowing the evidence trail to grow cold and shooters to go free. Turning in evidence to NIBIN labs greatly speeds up that process.
No single examiner made more than one error. Again, the overall false positive error rate was less than 1 percent. Study after study demonstrates the same reality: examiners are remarkably accurate when they identify casings and bullets.
Fingerprints are on a firearm as a result of oils from the skin adhering to the surface. Now, they are recoverable for about a year or so using the current standard recovery procedures used by the police.
They can test the firearm to determine if it is capable of discharging a cartridge or shotshell. They can also evaluate the mechanical operation of a firearm when there are allegations or concerns that the firearm discharged unintentionally.
Examination of the authorship of a written letter is considered the most common type of questioned document examination. Forensic document examiners may perform several tasks, including discerning if an item originated from the same source as a known item as well as the time a document was created.
Ballistics is the science that deals with the flight or movement of projectiles. There are four types of ballistics: internal, external, terminal and wound ballistics. Insight into these four areas of mechanical science will help you hit targets and select the best ammunition for your shooting sport or your hunt.
Our Ballistics Laboratory performs three different types of weapons examinations: Operability Studies, Serial Number Restorations and Microscopic Comparisons. Operability Studies are designed to determine if a weapon is capable of firing. This is an important issue when a case goes to trial.
By examining unique striations impressed into a bullet from the barrel of a gun, expended ammunition can be linked back to a specific weapon. These striations are due to the rifling inside the barrels of firearms. Rifling spins the bullet when it is fired out of the barrel to improve precision.
No single examiner made more than one error. Again, the overall false positive error rate was less than 1 percent. Study after study demonstrates the same reality: examiners are remarkably accurate when they identify casings and bullets.
Introduction: My name is Trent Wehner, I am a talented, brainy, zealous, light, funny, gleaming, attractive person who loves writing and wants to share my knowledge and understanding with you.
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