Forensic firearm examination is the forensic process of examining the characteristics of firearms or bullets left behind at a crime scene. Specialists in this field try to link bullets to weapons and weapons to individuals. They can raise and record obliterated serial numbers in an attempt to find the registered owner of a weapon and look for fingerprints on a weapon and cartridges.
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. Although bullet striations are individualized unique evidence, microscopic striations in the barrel of the weapon are subject to change slightly, after each round that is fired. For this reason, forensic ballistics examiners may not fire more than five shots from a weapon found at a scene. Known exemplars taken from a seized weapon can be compared to samples recovered from a scene using a comparison microscope as well as newer 3-D imaging technology. Striation images can also be uploaded to national databases. Furthermore, the markings can be compared to other images in an attempt to link one weapon to multiple crime scenes.
The ability to compare ammunition is a direct result of the invention of rifling around the turn of the 16th century. By forcing the bullet to spin as it travels down the barrel of the weapon the precision is greatly increased. At the same time, the rifling leaves marks on the bullet that are indicative of that particular barrel. Prior to mass production of firearms, each barrel and bullet mold was hand made by gunsmiths making them unique. The first successful documented case of forensic firearm examination occurred in 1835 when a member of the Bow Street Runners in London matched a recovered bullet from a murder victim to a specific mold in a suspect's home confirming that he made the bullet; this gave further evidence that the bullet maker was the perpetrator and he was convicted. As manufacturing and automation replaced hand tools, the ability to compare bullets became impossible due to the standardization of molds within a specific company. However, experts in the field postulated that there were microscopic differences on each barrel left during the manufacturing process. These differences were a result of wear on the machines and since each new weapon caused a tiny amount of wear, each barrel would be slightly different from every other barrel produced by that company. Also, each bullet fired from a specific barrel would be printed with the same marks, allowing investigators to identify the weapon that fired a specific bullet.
One of the first uses of this knowledge was in 1915 to exonerate Charles Stielow of the murder of his neighbors. Stielow was sentenced to death and appealed to Charles S. Whitman, the Governor of New York, who was not convinced by the evidence used to convict Stielow. Whitman halted the execution until an inquiry could be conducted and after further examination it was shown that Stielow's firearm could not have fired the bullets recovered from the victims. The invention of the comparison microscope by Calvin Goddard and Phillip O. Gravelle in 1925 modernized the forensic examination of firearms. Simultaneous comparison of two different objects at the same time allowed to closely examine striations for matches and therefore make a more definitive statement as to whether or not they matched.
In order to compare individual striations, examiners must obtain a known sample using the seized weapon. For slower-traveling bullets, such as pistols or revolvers, known bullet exemplars are created by firing the weapon into a water tank. The spent bullet can be recovered, intact, as the water slows down the bullet before it can reach the tank walls. For faster traveling bullets, such as those fired from high-powered rifles and military style weapons, water tanks cannot be used as the tank will not provide enough stopping power for the projectiles. To examine these weapons, investigators must fire them at a target at a controlled range with enough backing to stop the bullet and collect the spent round after it has been fired.
In the 1990s, there were two databases that were formed for storage of pictures of shell casings and bullets in gun crimes. The first was the Drugfire system which was used by the FBI. The second, the IBIS (Integrated Ballistic Identification System) was created by Forensic Technology, Inc. and eventually bought by the Alcohol Tobacco and Firearms (ATF) in 1993. The FBI and ATF realized that their systems would not work together, and they needed to find a way to share information between them. The NIBIN board was created in 1997, in hopes of creating one imaging system. A year after the creation of the NIBIN board, both the ATF and FBI decided to put their resources together toward one of the systems, and created the National Integrated Ballistics Information Network, with IBIS as the system.
Firearm examiners have attempted to determine the shooter's position by the location of spent bullet casings. The use of ejection pattern studies were originally part of incident reconstruction and methods for determining shooter location continue to be explained in major crime scene examination books. However, the validity of ejection pattern analysis has been brought into question by multiple studies that look at the reproducibility and end determination of shooter position by qualified examiners. Studies have shown that over 25% of spent casings land somewhere other than to the right and rear of the shooter. This is the most commonly accepted location for where spent cartridge casings should fall, and the large percentage of casings that end up somewhere else raises concerns for the validity of the examination technique. Investigators should only present a location gained from an ejection pattern study as a tentative estimate when using the information in a courtroom setting.
Prior to September 2005, comparative bullet-lead analysis was performed on bullets found at a scene that were too destroyed for striation comparison. The technique would attempt to determine the unique elemental breakdown of the bullet and compare it to seized bullets possessed by a suspect. Review of the method found that the breakdown of elements found in bullets could be significantly different enough to potentially allow for two bullets from separate sources to be correlated to each other. However, there are not enough differences to definitely match a bullet from a crime scene to one taken from a suspect's possession. An additional report in 2004 from the National Academy of Sciences (NAS) found that the testimony given regarding comparative bullet-lead analysis was overstated and potentially "misleading under the federal rules of evidence". In 2005, the Federal Bureau of Investigation indicated that they would no longer be performing comparative bullet-lead analysis.
In 2020 Itiel E. Dror and Nicholas Scurich looked at the validity of ballistic forensic experts when attempting to make an identification of a shell or bullet. They found that while some experts would come to the conclusion that the bullets were a definite match, another expert looking at the same evidence would determine it inconclusive. Dror and Scurich argue an "inconclusive" determination affects the error rate for the study, and provides very little confidence in the overall findings of the scientists. According to Dror and Scurich, the error rate, which was zero to one percent, could be higher. Their reasoning behind this is that if an "answer" was marked as inconclusive, it must count as a correct answer which decreases the error rate making it lower than it probably should be.They wondered how different the error rate would be if inconclusive was not an option. In addition, Dror and Scruich noted that the scientists seemed to come up with a more conclusive decision on the evidence if there was the added part of a human life hanging in the balance. In 2021 Alex Biederman and Kyriakos N. Kotsoglou responded to the Dror and Scurich paper and raised issues. Some of the issues raised by Biederman and Kotsoglou included: a paradox in which examiners' results agreed with ground truth but would be considered "error" via Dror and Scurich's proposals. Biederman and Kotsoglou also pointed out that Dror and Scurich's proposals would set false incentives where examiners would be directed to be "diving what the mythical forensic wisdom of the consensus opinion might (and hence enshrine the false belief in the existence of such wisdom), be rather than the ground truth". Biederman and Kotsoglou concluded "In all, our analysis does not leave much intact from recent attempts to label 'inconclusives as errors."
One way investigators have been able to link the string of shootings in the Washington, D.C., area is by analyzing the slugs that felled the victims. Here's an explanation of the technique, called ballistic fingerprinting, and a look at the debate surrounding the method.
Advocates for gun control want to expand the resources of ballistics investigators by creating a national computerized system for tracing bullets and shell casings to the guns that fired them. The system would require manufacturers to test-fire new guns before selling them to stores. Data detailing markings left on bullets by each weapon would then be entered into a computerized system known as IBIS.
Proponents say a national ballistic fingerprinting system would allow investigators who have found a bullet or bullets at the scene of a crime to enter data about the bullet's markings into the database and then quickly retrieve possible gun matches. This information could help lead them to the gun's buyer and possibly the perpetrator. 041b061a72