The National Institute of Standards and Technology (NIST) has come up with a new reference standard that will improve the way law enforcement agencies trace spent casings recovered at crime scenes to specific firearms.
Currently, when a spent casing is found at the scene of a crime, forensic examiners use a high-tech microscope – the Integrated Ballistic Identification System (IBIS) – to examine the “fingerprints” or signatures the firearm has left on the casing, i.e. the firing pin impression, the breech face impression and the ejector mark.
Lab technicians then create a digital copy of those signatures and catalogue those findings in a database called the National Integrated Ballistic Information Network (NIBIN).
Since no two firearms leave the exact same “fingerprints,” they can be used by law enforcement to track down a criminal or link a criminal to multiple crimes. Due to this fact, the margin for error is very small.
In other words, the methods by which forensic examiners match signatures from crime scene to the NIBIN better be sound and extremely precise. As such, NIST technicians are always looking for ways to refine and improve the system, hence the development of the new ballistic standard.
In a NIST press release, the engineers behind the new ballistic standard explained how it works:
The standard contains two items: an exact replica of a master cartridge case with distinct signature marks (obtained from the Department of Justice’s Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF), and a “golden” digital image of those same signatures that reside on the NIBIN.
Forensic labs can image the signatures on the SRM [Standard Reference Material] cartridge cases—a test of their optical microscope and measurement procedures—and compare those images to the golden image provided by ATF. In this way, lab technicians can verify their equipment is calibrated and functioning properly, validate their methodology and demonstrate that their work is traceable to an authoritative national standard.
Essentially, engineers create a clone copy of the cartridge with the signatures using a process called electroforming. This allows forensic examiners to make sure their digital renderings in the database are accurate.
“The electroforming process is so accurate that the replica cartridge cases made using it have signature marks that are less than a few micrometers—millionths of a meter—different from those on the master,” NIST mechanical engineer Alan Zheng, one of the team members who developed the reference casing, said in the press release.
If this process is a little unclear (which, admittedly it is), NIST physical science technician Brian Renegar, also a member of the ballistics SRM development team, gave a more explicit example of how the new standard works with respect to crime fighting.
“For instance, if a crime is committed in California, and another in New York using the same firearm, the link between the two crimes might be missed. The NIBIN network enables forensic examiners to identify these potential matches, or ‘hits’, where they might otherwise go unnoticed,” Renegar said in the press release.
“And the NIST ballistic SRMs [Standard Reference Material aka the new standard] ensure that the imaging systems used in the labs are calibrated and operating properly, and that proper measurement procedures are being followed.”