New Open Source 3D Database for Ballistics Toolmark Research

New Open Source 3D Database for Ballistics Toolmark Research

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Identifying the firearm used in a crime is more complicated than shown in the movies. However, the basic setup is correct. Ballistics examiners match bullets visually, and they have been doing it this way for almost 100 years.

According to Homeland Security News Wire, this month National Institute of Standards and Technology (NIST) released the largest open-access database of its kind — the NIST Ballistics Toolmark Research Database.

Led by Xiaoyu Alan Zheng, this database effort is partly in response to a 2009 report from the National Academy of Sciences, which highlighted the need for statistical methods to estimate uncertainty when matching ballistic and other types of forensic pattern evidence. The development of the database was largely funded with a grant from the National Institute of Justice.

When matching a bullet to a gun, examiners look at striations that are carved into the bullet by rifling in the gun’s barrel. If the cartridge case is left behind, they can also look at impressions left on it by the weapon’s breech face and firing pin.

But these clues can sometimes be misleading. Researchers would like to quantify this uncertainty using statistical methods, and to do that they need large databases of test-fired bullets and cartridge cases. The databases already in use for solving crimes, such as the National Integrated Ballistics Information Network (NIBIN), are proprietary and contain sensitive information. Researchers cannot download bulk data from them for use in statistical studies.

The NIST database, on the other hand, is open-access and the data is freely available.

To seed the database with data, Zheng went to forensics and law enforcement conferences asking agencies to test-fire every 9-mm firearm in their reference collection — 9 mm being the caliber most commonly used in the commission of crimes.  

After completing the test fires, labs sent the bullets and cartridge cases to Zheng at NIST, along with data on the gun that fired it. At the lab, technicians scanned these samples using a microscope that produces a high-resolution, 3-D topographic surface map — a virtual model of the physical object itself.

These surface maps produce more detailed comparison data than the two-dimensional images that are traditionally used to match bullets. For this reason, the field of forensic firearms identification is starting to make the transition to 3-D.

A standard file format for 3-D topographic surface maps has been agreed for use in ballistic imaging. NIST’s new research database will use this open standard, which will allow researchers to easily share data, though the database will also accept traditional two-dimensional images.

The database currently has only about 1,600 test fires — a relatively small number. “But, it’s like the first forensic DNA databases,” Zheng said. “They started off small but filled up quickly.”

In the meantime, the data that is available is already proving useful.

The database uses open source code, so researchers can check for bias or error in the algorithms, and correct any that are found.