Gunshot Residue Analysis (GSR)
Gunshot Residue Production and Analysis
Forensic investigations often rely on the evidence of gunshot and other firearms-related residues. When one fires a gun, the explosion creates a fine mist of particles. These particles consist of burnt and unburnt powder, as well as traces from the bullet, its casing, and the gun itself. As the mist settles, it lightly coats the area with gunshot residue. GSR will likely cling to the shooters hands, exposed skin, and clothing. Investigators typically sample this evidence with GSR test kit stubs. They can often obtain even more evidence from bullet-wipe deposits, partially burnt or unburnt powder, and trace materials on the bullet.
Microtrace’s experts test GSR and related residues using state-of-the-art analytical tools. Condensed particles of lead, antimony, and barium from the primer cap prove particularly useful for analytical purposes. The scientific community regards these “tri-component” particles as characteristic of a gunshot. Analyses typically begin with infrared photography and SEM analysis combined with energy dispersive X-ray spectroscopy (SEM/EDS). If a specific project calls for further analysis, our scientists can use advanced microchemical testing. When organic residue is present, it can be analyzed by gas chromatography and mass spectrometry (GC/MS).
GSR Case Reviews
Microtrace’s experts are routinely contacted to review the use of GSR and in criminal court proceedings. Our reviews consist of a critical examination of all aspects of a case. This can include sample collection, analytical details, interpretation, and testimony. The typical one-page reports issued by most labs often omit vast amounts of important details. Context is especially important when evidence from a suspect tests positive for tri-component particles; they are not a definitive indicator that a suspect has fired a weapon. The suspect may have been in the area of a discharged weapon, but not fired the shot themselves. Furthermore, secondary transfer of GSR can contaminate a suspect. Perhaps they shook hands with or were handcuffed by someone who had fired a gun. In some cases, careful characterization of the entire population of trace (residue) particles (and their morphologies) may suggest alternate explanations for the presence of tri-component particles.
Gunshot Residue Submissions
Microtrace has been providing rigorous and scientifically-supported analyses of GSR and providing expert testimony for more than 25 years. Our experience with gunshot residue analysis in a wide variety of environments has given us a unique and expert perspective when reviewing, re-analyzing, and conducting GSR tests for forensic purposes. We conduct all work in our ISO 17025 accredited laboratory.
Microtrace accepts and regularly analyzes commercial GSR test kits/collection kits. However, we specialize in unusual cases. We recognize that every investigation has its own sampling conditions and parameters. Because of this, our laboratory has developed the capabilities and expertise to accept a wide-variety of materials for testing and analysis. These include previously analyzed GSR collection kits/stubs, tape lifts, swabs, clothing, upholstery, window glass, and other materials from the vicinity of a suspected discharged firearm.
Our laboratory’s standard turn-around-time is 7-10 business days. However, Rush (3 business days) and Ultra-Rush (next day) options are also available.
Please contact us to discuss the specific needs of your project.
Gunshot Residue Standardized Methods
ASTM (American Society for Testing and Materials) wrote a standardized guide for the analysis of GSR. E1588; “Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive Spectrometry.”
SWGGSR (Scientific Working Group for Gunshot Residue) was the precursor to OSAC/ASTM (above). However, this group also wrote their own standardized guide for GSR analysis. “Guide for Primer Gunshot Residue Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry.” Download the guide here.
ENFSI (European Network of Forensic Science Institutes) working group on Firearms and GSR are working on a standardized guide for gunshot residue analysis for European laboratories.