3d images

How 3D Images Could Help Solve Future Gun Crimes

The three-dimensional technology aims to improve future forensic examinations of crimes involving firearms.

Matching a bullet to the firearm it was fired from is often the key to solving crimes. But the new technology aims to improve future forensic examinations of crimes involving firearms.

“Gun and tool mark analysis has been around since the 1920s,” said Alan Zheng, a mechanical engineer at the National Institute of Standards and Technology.

“It’s a science where a trained examiner can take a look at two fired bullets or two fired casings and try to relate them to a particular firearm.”



Zheng said the three-dimensional technology will modernize the way gun and tool mark analysis can be done.

When a bullet or cartridge case is recovered from a crime scene and the suspect’s firearm can be found, the firearm can be tested to compare whether the marks on the bullet or cartridge case cartridge correspond to the grooves of the barrel of the weapon.

“On the ball, they’re looking for streak patterns, which are basically parallel lines. Each barrel has been made or cut with rifling patterns, to help the bullet spin as it exits the barrel, which improves accuracy,” Zheng said. “Throughout this cutting process, you leave a lot of random features inside that barrel, so it’s almost like a fingerprint of that particular barrel.”

Currently, forensic scientists must have the bullets or cases in hand “which allows them to see two different bullets, side-by-side, in a sight, and try to match the patterns,” Zheng added.

A 3D topographic surface map of the base of a fired 9mm bullet. This visualization shows the grooves imprinted on the bullet by the barrel of the weapon that fired it. These 3D surface maps produce more detailed comparison data than the two-dimensional images traditionally used to match balls. (Courtesy of NIST)

Recently, NIST and the FBI worked with researchers to develop 3D surface scanning microscopes to produce 3D models, or virtual copies, of bullets. Computer algorithms then compare the microscopic characteristics of the two virtual balls to measure their similarity.

“It’s extremely accurate,” Zheng said. “You can select features in the micron range, less than one-hundredth the width of a human hair.”

Technology can help reviewers better understand what they are investigating.

“In the computer software, you can adjust the lighting and rotate the two different 3D datasets,” Zheng said.

A major process improvement is that forensic analysis and verification can be performed virtually.

“So now you can take the 3D data that you scanned and send it to another lab, and a separate reviewer can do that verification, without having access to the physical samples,” Zheng said.

As with any new technology used to solve crimes, courts will need to be satisfied that the technology is reliable.

“Usually when a new technology is used in forensics, there will be a landmark case that sets a precedent,” Zheng said.

In 1911, fingerprints were first accepted by US courts as a reliable means of identification. Courts began to allow DNA analysis to be admitted as evidence in the late 1980s.

Zheng expects the same to happen with 3D forensic technology.

“They go in and look at the basics of science. The judge must determine if the science is valid,” he said.

The Scientific Domain Committee Organization for Forensic Science, which is administered by NIST, has added two new standards to its registry of approved standards. The standards will provide guidance to crime labs implementing 3D methods.