The forensic procedure of studying the properties of firearms or bullets left behind at a crime scene is known as forensic firearm examination. Bullets are linked to weapons, and weapons are linked to individuals, according to experts in this field. In an attempt to locate the weapon’s registered owner, obliterated serial numbers can be raised and documented. The most commonly used reagent is nitric acid (HNO3). Fingerprints can also be found on the firearm and cartridges by examiners. Fingerprints are extremely important pieces of evidence. If prints are discovered at a crime scene, they will be dusted, photographed, gathered, and evaluated both by hand (using comparison microscopes) as well as compared with databases for possible references.
Firearms as Evidence
Every firearm tells the story, that firearms and ballistic marching play a vital part in criminal investigations. The information needed to convey their stories can be found on the outside and inside of a firearm. It is also found in ammunition and can be used to help with future investigations and prosecutions, as well as intelligence gathering and analysis.
At a crime scene, firearms and their surroundings might provide a range of evidence. These crime scenes can include but are not limited to any location where:
• A firearms-related injury has been suffered by a victim.
• A firearm has been discharged illegally.
• A firearm/firearm parts or components/ammunition/ammunition components suspected of being used in or linked to a crime have been discovered.
• Unlawfully made, converted, or test-fired firearms/firearm parts or components/ammunition
A ‘Crime Gun’ is a firearm that has been illegally obtained and/or used in the commission of a crime. Examining and tracing these objects may:
• It could confirm that the firearm is the source of shots fired during a crime.
• It enables the identification of persons of interest.
• It reveals links to related crimes.
• It indicates evidence of an illicit trafficking network.
• It indicates evidence of illicit manufacturing.
Evidence relating to firearms can be used both concerning the main crime and in the development of strong parallel criminal cases, such as international firearms trafficking. Occasionally, a single piece of evidence can help both investigations. A ballistic comparison, for example, can prove that a firearm was used in a murder case as well as other crimes committed in another country, which is already indicative of the firearm’s routing.
The value of evidence provided by firearms, ballistics, and ammunition is neglected; enforcement activities end at the point of seizure or recovery in many criminal investigations. However, firearm-related objects seized and recovered may give crucial evidence of a wide range of other offenses, including gun trafficking and illicit manufacturing.
Examination of the Firearm
Using cyanoacrylate (sometimes known as superglue) fuming, fingerprints can be recovered from the surface of weapons. Firearms are put in a fume hood that is designed to equally distribute fumes rather than remove them. Superglue liquid is placed in a container and heated until it becomes gaseous. The flowing gases adhere to the fingerprint’s oils, turning the print white. The white print that results can be enhanced with fingerprint powder to make it stand out more against the weapon’s finish.
While the fuming process is commonly used on recovered guns, recovering fingerprints from the surfaces of a handgun is difficult due to the textured grip and general state of recovered weapons. If fingerprints are recovered, fingerprint databases such as the Integrated Automated Fingerprint Identification System can be used to process them (IAFIS). Touch DNA left by whoever handled the weapon can also be analyzed in various areas of the recovered weapon. The tiny levels of DNA can be recovered.
Serial Number Recovery
After the United States approved the Gun Control Act of 1968, serial numbers became common. All guns manufactured in the country or imported into the country were required to have a serial number under this regulation. Many rifles did not have serial numbers or had serial numbers that were not unique and were reused by the same manufacturer on many firearms before 1968. Examiners can try to recover the original serial numbers if the serial numbers on a recovered weapon have been altered or destroyed.
Magnetic particle inspection and chemical restoration are the two basic procedures for restoring serial numbers. Because of the non-destructive nature of magnetic particle inspection, it is advised that it be done first. Chemical restoration is the next stage in the forensic analysis if magnetic particle inspection fails.
If the serial number is successfully restored, it can be utilized to assist investigators in tracking the weapon’s history and possibly determining who owns it. Investigators can use firearm databases like the National Crime Information Center of the United States and INTERPOL’s Firearm Reference Table to track down guns that have been lost, stolen, or used in other crimes.
Magnetic Particle Inspection
Magnetic particle inspection was created to detect faults or anomalies in magnetic materials, but it may now be used on rifles to visualize the serial number underneath the obliterated area. Examiners use a magnetic field to hold the weapon while doing this technique. When a solution of ferrous particles is applied to the weapon’s magnetized surface, the particles will be drawn to the distorted magnetic field and will build up in that location. If fluorescent particles are introduced to the ferrous solution, ultraviolet light can be used to help visualize any serial numbers that have been collected.
Chemical milling is a type of chemical restoration. Chemical milling is a method of gradually removing material to achieve the desired form. Small bits of metal are removed in serial number restoration until variations in the metal corresponding to the serial number are revealed. This is conceivable because the grain boundary structure beneath the metal’s surface is distorted when the numbers are stamped. Chemical restoration, on the other hand, is limited to that depth and is only effective when the serial number has been obliterated superficially. The place where the serial number used to be, is sanded first by examiners performing a restoration. This cleans up any debris left behind after the serial number was erased.
The examiner then selects a reagent, typically an acid, to slowly bring the number back to the surface. The type of chemical utilized is determined by the weapon’s construction. Fry’s Reagent for magnetic metal is one example of these acids.
Examination of Cartridges
Spent cartridges can be analyzed for physical evidence such as fingerprints or compared to samples that match them to a weapon if they are discovered at a crime scene. The unique tool marks left by various sections of the weapon, including the firing pin and ejector in semi and fully automatic rifles, are used to examine the cartridge. These markings can be compared to known exemplars fired from the same weapon and using the same components. A comparison microscope is used to examine the marks that have been left on the cartridge. Examiners compare the questioned cartridge to the known exemplar, looking for microscopic marks made during the firing process that are similar.
Examination of Bullets
By studying the overall features of a recovered bullet, a preliminary inspection of the bullet can exclude a wide number of guns. Several firearms can be quickly checked out as being incapable of shooting that type of bullet by determining general features of the fired ammunition. The weapon’s make and model can also be inferred from a combination of several class features that are shared by all manufacturers.
The lands and grooves, the bullet’s caliber, and the rifling twist are the three main class features of all bullets. All three are directly related to the type of barrel that fired the bullet. The bumps and valleys are generated when the rifling is created[presence of lands and grooves]. The caliber refers to the barrel’s diameter. The twist is the clockwise (right-handed) or counterclockwise (left-handed) direction of the striations left by the barrel’s rifling (left-handed). Except for guns made by the Colt Manufacturing Company, which have left-handed twists, most barrels will have a right-handed twist.
Individual characteristics of weapon barrels that match the class criteria of recovered bullets can be analyzed further to identify if the bullet came from that particular weapon.
Examiners must get a known sample using the seized weapon to compare specific striations. Known bullet exemplars are made by shooting slower-moving bullets, such as pistols or revolvers, into a water tank. Because the bullet slows down before it reaches the tank walls, the spent bullet can be collected intact. Water tanks cannot be used to stop faster-moving bullets, such as those fired from high-powered rifles and military-style weapons, because the tank will not provide adequate stopping power.
Investigators must fire these guns at a target at a controlled range with enough backing to stop the bullet and collect the spent round after it has been fired to analyze them.
Once a known exemplar has been created, the evidence sample can be compared to the known by using a comparison microscope to examine both at the same time. Striations that line up are looked at more attentively to see if there are numerous matches in a row. Examiners are taught to use the phrase “sufficient agreement” when testifying because there is no set number of successive matches that translates to a match declaration. An examiner’s ability to make that judgment is determined by their training and experience. During testimony in court, both the prosecution and the defense will question the examiners’ conclusions.
How the Samples are Collected?
Evidence of firearms can be recovered in a variety of ways and locations. Crime scene investigators can recover firearms from shooting scenes and send them to a laboratory for analysis. Bullets, bullet fragments, cartridge cases, shot shell wadding, and other items are often collected individually and sent to a laboratory after proper documentation / photography. Evidence of bullets can also be obtained at an autopsy or in an emergency room. In these situations, the material should be labeled as a biohazard and delivered to the lab. For packaging and submitting evidence, each laboratory has written procedures.
Bullets and slugs that do not hit a person are frequently embedded in a surrounding surface like wood or drywall. Cutting out a section of the substance and sending it to the lab for a weapons examiner to properly extract it is the best way to acquire this evidence. This prevents any markings from being added or destroyed that could be important in identifying or matching the suspected firearm.
Who Conducts the Analysis?
This evidence should be evaluated and compared by a well-trained weapons examiner. These examiners will have had comprehensive training in firearms and ammunition production, as well as evidence detection, recovery, handling, and examination processes, comparative microscope equipment and techniques, courtroom testimony and legal issues, and casework.
Most state crime laboratories in the United States have a firearms examiner or examiners on staff who may perform analysis for local police agencies if the need arises. Some police departments use a qualified examiner.
How and Where the Analysis is Performed?
The majority of exams are carried out by crime laboratory personnel who have been trained to do so. Some private laboratories/companies can perform this type of examination. Whatever option is chosen, the evidence, as well as any firearms seized, must be submitted for review following the submitting agency’s regulations and procedures.
Actual objects of evidence are sent to either crime laboratories or private laboratories, depending on the policies and procedures of the seeking agency. These items should be submitted following proper chain-of-custody procedures.
Certain items of equipment will be available in the laboratory to conduct the appropriate examinations. Bullet evidence is weighed and measured using measuring devices such as calipers and balances. The basic class features of fired bullets, bullet fragments, and cartridge/shot shell cases are determined using stereo microscopes.
Fired bullets, bullet fragments, and cartridge/shot shell cases are examined using a comparison microscope. The above materials, as well as special equipment to measure the firearm’s trigger pull and check the interior of the barrel, are utilized in the testing of weapons. There must also be facilities to test-fire and recover fired bullets and cartridge cases for the submitted firearm. The majority of laboratories employ a water recovery procedure, which entails dumping the handgun into a big tank of water with a port. Other techniques, such as metal boxes housing cotton waste material, are also employed.