Forensic firearm examination
By examining unique striations impressed into a bullet from the barrel of a gun, expended ammunition can be linked back to a specific weapon.
[3] 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.
Prior to mass production of firearms, each barrel and bullet mold was hand made by gunsmiths making them unique.
[6] As manufacturing and automation replaced hand tools, the ability to compare bullets became impossible due to the standardization of molds within a specific company.
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.
[9] The invention of the comparison microscope by Calvin Goddard and Phillip O. Gravelle in 1925 modernized the forensic examination of firearms.
[12] The investigation stalled until December 1929 when Fred Burke, a member of the Egan's Rats, shot and killed a police officer in St. Joseph, Michigan.
After test firing the guns, Goddard proved that the weapons were those used to kill the members of the North Side Gang, absolving the Chicago police department of all involvement.
[12] The successful use of Goddard's technique resulted in the solidification of his place as the father of forensic firearm examination.
However, the low levels of DNA that can be recovered presents numerous issues such as contamination and analysis anomalies such as allele drop-out and drop-in.
[26] If fluorescent particles are added to the ferrous solution, ultraviolet light can be used to make it easier to visualize any recovered serial number.
[21] Spent cartridges found at a scene can be examined for physical evidence such as fingerprints or compared to samples that match them to a weapon.
The examination of the cartridge relies on the unique tool marks left by the various parts of the weapon including the firing pin and the ejector in semi and fully automatic firearms.
Examiners view the questioned cartridge and the known exemplar simultaneously, looking for similar microscopic marks left during the firing process.
[30]: 152 Cartridges are also routinely examined for fingerprints as the act of loading the ammunition into the magazine, or chamber, leaves recoverable impressions.
Each firing pin would have a unique serial number allowing investigators to trace casings found at a crime scene to a known firearm.
[33] The law, and microstamping in general, has received significant opposition from gun manufacturers due the technology being unreliable, and not proven to aid in preventing or solving crimes.
The make and model of the weapon can also be inferred from the combination of different class characteristics that are common to specific manufactures.
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 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.
[45] 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.
Investigators should only present a location gained from an ejection pattern study as a tentative estimate when using the information in a courtroom setting.
[46] Prior to September 2005, comparative bullet-lead analysis was performed on bullets found at a scene that were too destroyed for striation comparison.
[48] 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".
The report's section on firearm examination focused on the lack of defined requirements that are necessary in order to determine "matches" between known and unknown striations.
"[30]: 154 Without defined procedures on what is and what isn't considered "sufficient agreement" the report states that forensic firearm examination contains fundamental problems that need to be addressed by the forensic community through a set of repeatable scientific studies that outline standard operating procedures that should be adopted by all firearm examiners.
[50] 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.
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.
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.
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.
