Gunshot residue (GSR) is an evidence of major importance in firearm-related crimes. The recent introduction of nontoxic ammunition has made impossible the characterization of GSR particles by the current methods employed by forensic experts. To overcome this drawback, the introduction of luminescent markers was proposed, allowing on-site visual detection of luminescent gunshot residue (LGSR) at the crime scene. Three different luminescent markers coordinated with europium for specific and selective encoding of ammunition have been proposed. To promote a variety of versatile tools for GSR analysis, spectroscopic techniques combined with chemometric methods can be applied to achieve a reliable, fast, and nondestructive means to identify LGSR and discriminate among the different markers. Luminescence (emission and excitation), normal, and resonance Raman spectroscopies associated with principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were evaluated. The classification model using the complementary information on emission and excitation spectra, a.k.a. data fusion, provided a 100% correct classification for all markers. A comprehensive study has been developed to show that the insertion of luminescent markers enables not only the easy localization of GSR residues but also the possibility of ammunition encoding through the use of multivariate classification methods.

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The identification and analysis of documentary fraud is always a challenge for forensic science. Document analysis has proven to be an important branch of forensics in elucidating the authenticity of documents. The development and incorporation of luminescent inks in authentic documents have proved to be an excellent security feature. This paper purposes the use of a possible luminescent ink marker for anti-counterfeiting applications, aiming to create a document encoding process that is simple, robust, sensitive, and non-destructive. Since luminescent inks markers provide a visual, chemical, and spectral signature, and can be easily detected by using a UV lamp, the aid of unsupervised chemometric tools makes it possible to differentiate the luminescent markers inserted in the ink. Unsupervised models of principal component analysis (PCA) and K-mean were successful in correctly associating marked inks with their respective pure markers, while a supervised classification model based on partial least squares discriminant analysis (PLS-DA) correctly classified all samples from the prediction set and the blind test samples. For comparison, a soft independent modeling of class analogy (SIMCA) model was also built, which despite showing a misclassified sample it is also a strong candidate for future applications.

Gunshot residues (GSR) are one of the most important forensic traces in crimes involving firearm discharge, being the conventional GSR characterized by containing spheroidal particles composed of Pb, Ba, and Sb. Over the years, a wide range of techniques has been applied and improved to characterize the conventional GSR, with deserved emphasis on scanning electron microscopy coupled with energy‐dispersive x‐ray spectroscopy (SEM/EDS). However, the introduction of nontoxic ammunition (NTA), or heavy metal‐free (HMF), on the market has triggered a search for new methodologies for GSR identification since methods based on the chemical and/or morphological profiles of conventional GSR are no longer appropriate for the analysis of this type of residues. This review highlights current methods and proposals for characterization of GSR from NTA, which involve either the search for characteristic chemical profiles or the insertion of selective markers in this new type of ammunition. This article is categorized under: Forensic Chemistry and Trace Evidence > Emerging Technologies and Methods Forensic Medicine > Imaging Modalities

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