Firearm Forensics
Gun crime is not going away, but current forensic tools are limited at best. We believe that attenuated total reflectance (ATR) imaging could fill a big gap in the crime scene investigator’s armory.
According to the Center for Disease Control, firearm related shootings were responsible for over 68 percent of homicides and were one of the three leading causes of injury-related deaths in the United States in 2011. Shootings were also the second leading cause of law enforcement officer deaths in 2010. Given these facts, we believe that a rapid, high-throughput analytical tool for the detection and analysis of trace firearm evidence is long overdue.
Forensic investigators usually rely on the collection of some sort of ballistics evidence, whether it is the actual firearm, cartridge case or projectile, to link a suspect to a firearms crime. Tool mark and impression identifications match physical markings left on cartridge cases or projectiles to markings on the firearms. While this technique is the most popular tool used by ballistic investigators, it is subjective by nature; a tool mark examiner is required to interpret certain observations. These comparisons are susceptible to high rates of error (over 10 percent) and variability because different examiners have different levels of training and experience. Given these shortcomings, we feel that tool mark examinations are not appropriate to determine whether ballistics evidence matches materials recovered from the suspect. Rather, the ideal tool would target crime scene shooting incident reconstruction through gunshot residue (GSR) analysis.
Although GSR trace evidence is associated with each and every firearm discharge, there is no current analytical technique for the elucidation of forensically relevant information which a crime scene sample has to offer. Current techniques are only suitable for GSR particles originating from the primer of the ammunition and target just a few heavy metals.
Unfortunately, GSR samples originating from “heavy metal free” or “green” ammunition are void of these metals and thus current methodology is not appropriate for the analysis of these sample. Therefore, we believe there is a need in the forensic science community for a more specific method of GSR detection.
Our approach uses attenuated total reflectance (ATR)-imaging, which targets a much wider range of chemicals including GSR particles originating from both the primer and propellant of the ammunition (2), for the rapid detection of GSR. ATR-imaging requires absolutely no sample preparation (it simply requires pressing some common double-sided office tape against a surface populated with GSR) and, most importantly, it is non-destructive, which allows for multiple analyses or re-analyses to be performed on the sample – the ability to preserve forensic evidence is always of paramount importance.
ATR imaging combines the specificity of vibrational spectroscopy (measuring the molecular fingerprint of the analyte) with the convenience of automated microspectroscopic mapping. ATR imaging uses a germanium crystal in contact with the sample surface, which offers increased spatial resolution compared with other spectroscopic mapping techniques, meaning that we can lower the limit of detection – or decrease the size of GSR particles that can be resolved on the tape substrate. Chemical maps can be generated from the spectroscopic images that clearly visualize detected GSR particles that are hidden when a visual inspection is used.
When fully developed, the combined approach of tape-lifting and ATR imaging will allow forensic investigators to rapidly collect and detect GSR particles from the body or clothing of a suspected shooter. If GSR is detected, it has the potential to link the suspect to the crime scene, whilst its absence could equally exonerate an innocent person.
Where are we now? Well, we need to study the specificity of the approach with regards to potential false-positive contaminants. In addition, we must examine the effect of chemical composition of the propellant, primer, projectile and cartridge case, as well as the type of firearm and firing mechanism, on the spectroscopic signature of GSR. Beyond GSR analysis, we believe that the technique could have many applications in counter-terrorism and homeland security, including explosives detection. Unfortunately, there is no escaping the fact that violent crime will continue indefinitely and we analytical chemists must play our part in the battle against it.
- J. Bueno and I. K. Lednev, “Attenuated Total Reflectance-FT-IR Imaging for Rapid and Automated Detection of Gunshot Residue”, Anal. Chem. 86 (7), 3389–3396 (2014).
Building new instruments and developing new methods at the Moscow Institute of Physics and Technology gave Igor Lednev the experience that he needed to tackle some major practical problems in chemistry and biochemistry. After publishing over 160 peer reviewed articles on fundamental science, he and his students have developed a new method that could make a significant contribution to practical forensics.
Justin Bueno’s pursuit of an advanced degree at the University at Albany, SUNY was determined mostly by coincidence. “I always loved watching documentaries on forensic science, but I was often left wanting a more in-depth description of the analytical techniques; luckily, Dr. Lednev had an opening in his research lab that meshed both analytical and forensic chemistries perfectly.”The research performed by Bueno in Lednev’s lab earned him a PhD in analytical chemistry in 2013. “I could have never dreamed that the project I started in 2009 would possess the great potential to be a tool that real world forensic investigators use.”
