This webinar originally occurred on November 20, 2019
Duration: 1.5 hours
Forensic laboratories and law enforcement personnel provide valuable support in the reconstruction of events and the assessment of the value of evidence in firearm-related investigations. The scientific validity of this field relies on extensive research and standardization of the existing methods (i.e., ASTM 1588-17 SEM-EDS). Nonetheless, there are still some challenges in this arena in terms of speed of analysis, preservation of evidence, accuracy, and interpretation of results. The main goal of this webinar was to present a discussion of the current state of gunshot residue (GSR) detection and efforts being made to improve current capabilities.
This webinar presented the development and validation of novel methods to identify organic and inorganic gunshot residues. Electrochemical and laser-based spectroscopic techniques (LIBS) are presented as screening methods that are quicker, more selective, and more powerful than any current field-testing technique. The analysis is conducted sequentially on universal SEM-EDS carbon-stub adhesives, in less than 5 minutes per sample, and with minimal destruction of the sample. These methods offer superior information via simultaneous detection of organic and inorganic components and identification of a significant number of elements used in modern ammunition (standard and “green” non-toxic ammunition).
The proposed methodologies were validated through a set of 500 samples and in-house GSR control standards. In this study, authentic samples were collected from hands traced from background populations and from the hands of shooters who fired a gun. These screening methods demonstrated low false positives and false negatives. Information on inorganic GSR and organic GSR markers was possible on the same sample, with accuracy greater than 87%. Moreover, LIBS can generate 3D-chemical images of the spatial distribution of GSR on the sample for enhanced confidence in the results. These methods have the potential to be adopted in forensic laboratories and the field, with the capability to accelerate response time and reduce backlogs and unnecessary incarceration costs.
Also, a novel LC/MS method that utilizes crown ether complexation for inorganic and organic detection was optimized as a modern tool for confirmation purposes and to cross-validate the performance of the screening tests. These assays are expected to offer a cost-effective approach to complement the traditional SEM-EDS method widely utilized in forensic laboratories.
The resulting data was assessed using different statistical approaches—critical threshold, Logistic Regression, Naïve Bayes, and Neural Networks —to examine the performance of each method alone and collectively. Experiments were designed to assess error rates, selectivity, sensitivity, and accuracy. Probabilistic assessments from population studies are anticipated to assist forensic examiners and the trier of fact to make informed decisions about the significance of the evidence.
Detailed Learning Objectives
- Understand challenges faced in the forensic analysis and interpretation of gunshot residues and how emerging technologies can provide viable solutions.
- Recognize the main capabilities and limitation of electrochemistry, LIBS and LC/MS for GSR detection and their potential impact to the criminal justice.
- Identify the value of using populations that simulate casework samples for the validation and assessment of performance measures of qualitative data.
- Dr. Tatiana Trejos
- Dr. Luis Arroyo
- Dr. Suzanne Bell
Funding for this Forensic Technology Center of Excellence webinar has been provided by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice.
The opinions, findings, and conclusions or recommendations expressed in this webinar are those of the presenter(s) and do not necessarily reflect those of the U.S. Department of Justice.