A mixed composition particle highlights the formation mechanism of the weapon memory effect phenomenon

Pervasiveness of inorganic gunshot residue (IGSR) in handguns after cleaning and conditioning procedures

Memory effect in firearms that is, the possibility for a weapon to release inorganic particles whose elemental composition depends on its entire shooting history, is responsible for most of the interpretation difficulties encountered in forensic gunshot residue analysis. The presence of residues chemically inconsistent with the last discharged round, the creation of particles having unusual elemental profiles, and the dependence of residue population composition on the collection point are all manifestations of memory effect. The experimental results reported in this paper highlight the ineffectiveness of a wide number of gun cleaning procedures in reducing memory effect. Moreover, the common alternative of discharging batches of rounds having a "new" primer mixture does not fully eliminate the possibility to recover "old" residues at least from the shooter's hands. Two brand new pistols and ammunition having lead-based, leadless and heavy metal free primers were used. Specimens, collected both from the shooters' hands and from cotton targets set nearby the gun muzzle, were analyzed by SEM-EDS and by ICP-OES. After discharging 10's of new ammunitions, the number of old residues ejected from the gun muzzle indeed showed an asymptotic decrease to zero. In spite of this, the number of old residues recovered from the shooter's hands did not follow any predictable trend. These different behaviors suggest that all internal components of a gun, and not just the barrel, play a role in memory effect.

Strontium in barium sulphate as a discriminating factor in the forensic analysis of tool paint by SEM/EDS

In the context of forensic tool paint analysis, the development of analytical strategies to distinguish between different tools is of great interest in order to form a better opinion on whether or not a trace of paint seized at a crime scene originates from a tool found, for example, during a search of a house. A study was therefore conducted on the potential of using X-ray mapping to discriminate red tools that are not otherwise distinguished by standard analytical techniques (i.e. optical microscopy, infra-red spectroscopy, Raman spectroscopy). In this study, the presence of trace amounts of strontium - revealed by X-ray mapping - in the main mineral filler, namely barium sulphate, allowed the discrimination of different tools using a statistical approach. This study is one example among others of the potential of X-ray mapping for a better characterisation of tool paints in a forensic context.

Interpol review of gunshot residue 2016-2019

This review paper covers the forensic-relevant literature in gunshot residue analysis from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Conduction of a round-robin test on a real sample for the identification of gunshot residues by SEM/EDX

A round-robin test on the identification of GSR particles by SEM/EDX and involving eleven Institutes was conducted on a real sample, in order to evaluate the possibilities/limitations of using such sample to get additional information (compared to the analysis of the usual synthetic sample used within the framework of the ENFSI proficiency test) about the performances of the SEM/EDX systems. Each Institute was asked to analyse this sample following its own standard operating procedure, and by using all the systems in house, whenever available. Between each Institute, a check of the sample was performed by the organizing Institute (NICC), in order inter alia to monitor any degradation and/or contamination of the sample. A total of about 30 analyses were performed on the sample. For each particle of interest identified on the real sample, the detection effectiveness was monitored, as well as the classification allotted by each Institute. The Institutes were also asked to report some of their measurement parameters, and to send the results as they would have been communicated in their own case report. A quite good agreement was observed with regard to the classification of the particles of interest, since a broad consensus was reached for approximately 75% of these particles. A different classification risk exists for some classes, the barium/antimony classes being probably the most critical, as traces of lead may cause the particles to shift (or not) from the consistent with GSR upper-class to the characteristic of GSR upper-class; in the end, the decision to shift from one class to another strongly depends on local rules. At the end of the campaign, a survey sent to collect experience and lessons learned from this exercise showed that analysing a real sample definitively offers an added value, especially in terms of classification process (during the automatic run and when performing the manual review) of particles.