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Gunshot Residue Matching Puts Shooters in Sights

Technology that matches gunshot residue with specific ammunition brands is helping to close the loop on firearms offenders. Gunshot residue is commonly found on the clothing of the shooter and around the wound site of the gunshot victim.

Researchers from Flinders University in South Australia have used technology borrowed from the mining industry to match glass fragments from gunshot residue with specific ammunition. They found a majority of ammunition contained glass fragments that showed up in gunshot residue.

This method has now been used to link the residue with specific ammunition brands. It is an area there has been little research in as previous investigations focused on bullet casings.

Lead researcher Prof Paul Kirkbride said the research would change the way global law enforcement agencies identified shooters. “The gun crime in the United States is mainly high calibre or high calibre handguns, and there are different ammunition types that do have ground glass in them and we are trying to now investigate those,” he said.

“We realised that the glass that is present is likely to survive through the firing process and left unchanged. We found that ammunition is unique and effectively has a sort of fingerprint on the glass.”

Kirkbride said other methods had too many variables and were not as reliable. “A print on a cartridge case could always point to the type of gun and then the individual gun. A bullet that comes out of a gun will have marks on it and that will allow you to again say which type of gun was used.

“Of course, if a shooter sees a case come out of the weapon they can always take it away from the crime scene, and a bullet could have gone anywhere and can be really difficult to recover.

“There is always a lot of refinement that is necessary and there may be some new techniques we can explore to see if it can be done faster or cheaper. But if those two things are gone this is a new way to link the shooting to the individual or the bullet.”

Glass fragments are collected from a crime scene with adhesive tape and then processed using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). This method – more commonly found in the mining industry to identify granules – works by shining a tiny beam of light onto the residue. It is then able to identify the amount of sodium, barium or lithium present in the glass.

“Sometimes it works beautifully, but sometimes multiple brands look alike,” Kirkbride said. “In the future we hope to match all ammunition to all brands, but we are just working our way through that now.”

The use of glass in bullets is not universal but it is used in a large percentage of high-calibre weapons and the majority of 0.22-calibre handguns.

The United States has more firearm deaths per year than any other developed nation – there are almost as many guns in the country as there are people. According to the Gun Violence Archive, about 13,286 people were killed in the United States by firearms in 2015 and 26,819 people were injured.

Caleb Radford Adapted from The Lead South Australia / CC by 4.0