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Advent of ‘Green’ Ammunition Prompts Forensic Science to Analyze Organic and Inorganic Gunshot Residue and Establish Benchmarks for CSI

by Jo Ellen Nott

In the July 2023 issue of the Forensic Chemistry journal, new research from West Virginia University (“WVU”) forensic scientists reveals that gunshot residue (“GSR”) behaves differently on skin, hair, and fabric depending on whether it contains organic or inorganic compounds. The WVU scientists are working to establish benchmarks for analyzing organic GSR which will, in turn, expand the capabilities of GSR testing.

When a gun is fired, two kinds of residue are created: organic and inorganic. Inorganic residues come from the metallic components of the firearm (the bullet and the casing), as well as from the primer, which is the mix of chemicals that detonates the propellant. The typical inorganic particles found in GSR are lead, barium, and antimony. Organic residues are created by the propellant which explodes to force the bullet out of the firearm’s barrel. The typical organic particles found in GSR are the complex hydrocarbons nitroglycerin and diphenylamine.

The WVU researchers found inorganic GSR particles last longer on a surface, whether it be skin or fabric, than organic compounds. The downside of testing for inorganic GSR is that it is more susceptible to being lost or transferred by common activities. For example, a shooter who washes his hands with soap and water, then dries them with a paper towel, will likely not present lead, barium, and antimony particles on his hands.

Tatiana Trejos, associate professor in the Department of Forensic and Investigative Science and one of the leads on the organic GSR research, says that the surface persistence and loss to outside forces of inorganic GSR particles “can be critical to questions about whether someone is the victim of a suicide or homicide.”

On the other hand, the particles of organic GSR can be lost from clothing if a suspect struggles during arrest, but they are less likely to transfer to someone else, like the arresting officer. In contrast to inorganic particles, organic particles disappear over time due to factors like evaporation from the skin. Another important difference is that organic compounds do not transfer at all whereas “up to 100 characteristic inorganic particles can transfer from one person to another during a handshake.”

The WVU researchers have developed a new method for analyzing GSR at crime scenes that could be used in conjunction with their findings on the behavior of organic and inorganic compounds. This method will allow crime scene investigators to get results more quickly and make more informed decisions about whether a suspect has fired a gun.

The WVU research is expected to have a significant impact on the way GSR is analyzed in criminal cases. Trejos believes that by providing faster and more informative investigative tools, her group’s research will help apprehend offenders with more solid evidence and minimize the potential for false incarcerations.  

Sources: Forensic Magazine, RTI International, Science Direct

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