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.

Implementation and Optimization of the Sodium-Rhodizonate Method for Chemographic Shooting Distance Estimation.

In shooting incident investigations where it is important to estimate the shooting distance, the sodium-rhodizonate coloring method has been used for the visualization of GSR patterns extensively. This publication describes the optimization of this method by the use of a heated press for the transfer of GSR traces on garments, as well as variation of a number of other important process parameters. Our final aim for this project was to prepare a formal validation of the coloring method as prerequisite for its inclusion into the scope of ISO17025-certified methods in the GSR Laboratory. A number of important factors and process parameters were identified, such as buffer composition and pH, type of textile used as a substrate and resolution of the documentation of the results. Results were tested using a synthetic proficiency test. Our optimized method has been found to be a very effective technique for visualization of macroscopic GSR traces.

Automatic forensic analysis of automotive paints using optical microscopy.

The timely identification of vehicles involved in an accident, such as a hit-and-run situation, bears great importance in forensics. To this end, procedures have been defined for analyzing car paint samples that combine techniques such as visual analysis and Fourier transform infrared spectroscopy. This work proposes a new methodology in order to automate the visual analysis using image retrieval. Specifically, color and texture information is extracted from a microscopic image of a recovered paint sample, and this information is then compared with the same features for a database of paint types, resulting in a shortlist of candidate paints. In order to demonstrate the operation of the methodology, a test database has been set up and two retrieval experiments have been performed. The first experiment quantifies the performance of the procedure for retrieving exact matches, while the second experiment emulates the real-life situation of paint samples that experience changes in color and texture over time.

Primer composition and memory effect of weapons--some trends from a systematic approach in casework.

Since 2008, our laboratory has adopted a systematic approach to the examination of gunshot residues (GSR) in casework by analysing, whenever possible, the inorganic composition present in ammunition (cartridge cases and unused ammunition). By compiling the results of these analyses in a database, it is possible to observe some trends during the period of interest: on the one hand, the prevalence of primers containing lead, barium and antimony is about 50%, and even as high as 70% when including lead-barium-antimony based primers also containing tin; on the other hand, the prevalence of non-toxic primers is for the time being very low. Still using the same approach, test firings were performed with recovered weapons and litigious ammunition whenever possible in order to estimate the influence of the well known "memory effect" of the weapons on the GSR analysis results. The first results show a quite strong memory effect for the .22 and the .32 caliber, unlike the .38 caliber. This is probably due to a high prevalence of lead-barium-antimony based primers for the latter caliber.

Development of a quantitative LC-MS/MS method for the analysis of common propellant powder stabilizers in gunshot residue.

In traditional scanning electron microscopy/energy dispersive X-ray analysis of gunshot residue (GSR), one has to cope more and more frequently with limitations of this technique due to the use of lead-free ammunition or ammunition lacking heavy metals. New methods for the analysis of the organic components of common propellant powder stabilizers were developed based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). A multiple reactions monitoring scanning method was created for the screening of akardite II, ethylcentralite, diphenylamine, methylcentralite, N-nitrosodiphenylamine, 2-nitrodiphenylamine, and 4-nitrodiphenylamine, present in standards mixtures. Five out of seven of these target compounds can be selectively identified and distinguished from the two others with a high accuracy. Samples from the hands of a shooter were collected by swabbing and underwent solid phase extraction prior to analysis. Detection limits ranging from 5 to 115 mug injected were achieved. Results from several firing trials show that the LC-MS/MS method is suitable for the detection of stabilizers in samples collected following the firing of 9 mm Para ammunitions.