Classification Improvements in Automated Gunshot Residue (GSR) Scans

Abstract

Classification of particles as gunshot residues (GSRs) is conducted using a semiautomatic approach in which the system first classifies particles based on an automatic elemental analysis, and then, examiners manually analyze particles having compositions which are characteristic of or consistent with GSRs. Analyzing all the particles in the second stage is time consuming with many particles classified by the initial automated system as being potentially GSRs excluded as such by the forensic examiner. In this paper, a new algorithm is developed to improve the initial classification step. The algorithm is based on a binary tree that was trained on almost 16,000 particles from 43 stubs used to sample hands of suspects. The classification algorithm was tested on 5,900 particles from 23 independent stubs and performed very well in terms of false positive and false negative rates. A routine use of the new algorithm can reduce significantly the analysis time of GSRs.

A study of the effect of working parameters and validation of SEM/EDS method for determination of elemental composition of commonly encountered GSR samples in shooting events in Kosovo

“…In the R Kosovo, all inorganic GSR samples have been identified by SEM/EDS. Innovations in instrument technology, automatisation of analysis, improvements in image processing and EDS spectra treatment software, as well as statistical approaches enlarged the possibility of SEM/EDS analysis and significance of interpretation of the obtained data [3,4]. However, strict monitoring of instrument sub-system performance and method validation to demonstrate the whole system behavior needed in order to guarantee the reliability of inorganic gunshot residue (iGSR) results presented in front of the justice authorities [13].…”

“…SEM/EDS was used to monitor GSR fate and persistence on the surfaces as hands, face, clothing or shot surrounding environment [22]. It was well recognized that operating parameters of SEM/EDS instruments as: working distance, electron beam accelerating voltage, beam current, magnification, scanning resolution affected the total number of detected particles [4]. Although the standard methods recommended some operating parameters, optimization of working parameters of individual instrument in each laboratory presented a possibility to increase the sensitivity and reliability of the analytical data.…”

“…An additional advantage is the non-destructive analysis, which allows the sample to be preserved as a legal proof. Increasing reliability of SEM/EDS analysis and reducing false positive (FP) and false negative results are connected to the possibility for revisit the specific or suspicious particles after automatic identification and re-study particle morphology and elemental composition [4,5]. When an evidence from shooting event is presented as characteristic GSR particle, attention must be paid to the analytical characteristics of the applied SEM/EDS protocol and quality control procedures after method validation [12][13][14].…”

“…When an evidence from shooting event is presented as characteristic GSR particle, attention must be paid to the analytical characteristics of the applied SEM/EDS protocol and quality control procedures after method validation [12–14]. It is well known that working parameters of SEM/EDS instrument affect the total number of detected GSR particles and therefore, should be carefully studied and optimized for each instrument and laboratory needs [4]. A detailed systematic guide for testing SEM/EDS behavior and identifying possible misbehavior of instruments’ sub‐systems have been recently proposed [13].…”

“…A recently published research has stated "finding one or two GSR particles had limited evidential value" [3]. However, the improvements in SEM/EDS technology combined with appropriate statistical approaches for data treatment highly increase the sensitivity of measurement and nowadays GSR particles with low dimensions and weight can be reliably detected [3,4]. These research findings impose for a sensitive detection of SEM/EDS by careful optimization of working parameters, on the one hand, and, on the other hand, a thorough validation of SEM/ EDS method for determination of GSR.…”