ESTIMATING THE TIME SINCE DISCHARGE OF HANDGUN CARTRIDGES USING A NOVEL HEADSPACE SORPTIVE EXTRACTION (HSSE) APPROACH

Estimating the time since discharge of handgun cartridges may be a useful piece of information in the forensic investigation of firearm-related crimes. Many approaches were reported throughout the last century. The most promising were generally based on analysing over time the decrease in the headspace concentration of dissipating compounds released during the discharge (especially, the most volatile ones, such as naphthalene). Following the good results obtained in analogous applications (i.e., the estimation of the time since last discharge of firearms and shotgun shells), headspace solid phase micro-extraction (SPME) followed by gas chromatography was recently suggested to analyse shot handgun cartridges. However, unsatisfactory results were reported, likely because of analytical limitations (reproducibility and sensitivity issues) and/or weak choices in target compounds and interpretative models. In an attempt to further study the potential of headspace analysis to estimate the time since discharge of handgun cartridges, a novel approach was developed in this PhD research. This was based on the extraction of fired cases by headspace sorptive extraction (HSSE), which is more exhaustive (and thus, more reproducible and sensitive) than SPME. Target compounds were selected on the basis of a preliminary study, and the entire analytical methodology was then optimized using a multivariate statistical approach based on the design-ofexperiments theory. Results showed good analytical performances in terms of detection limits and repeatability. Its application to real specimens revealed that the amounts of volatile GSR compounds rapidly decreased in the first hours after discharge (< 10 h), but they did not totally disappear from cartridge headspaces. Thus, through multivariate interpretation models, it was possible to provide time-since-discharge estimates up to 48 h and to differentiate recently fired cases from older ones. The best combinations of pretreatments and multivariate regression models were pairwise ratios followed by logarithm transformation (i.e., PLR) and random forests (RF) and/or partial least squares (PLS). The effects of several influential factors (i.e., cartridge position, humidity and temperature) were further studied. While all affected in some way the ageing kinetics of the single GSR compounds, they did not affect the multivariate models' dating accuracy, as long as there was no significant difference between reference and examined material. An evaluative model was also developed and allowed assigning a likelihood ratio to analytical outcomes given alternative hypotheses on the time since discharge forwarded by the parties at trial. Thus, headspace analysis of spent cartridges was found to provide helpful evidence to assist forensic practitioners in answering questions about time since discharge. Further research is needed, but results toward the development of a complete dating methodology, and its implementation in real forensic cases, are promising. -- Estimer le temps depuis la décharge des douilles peut être une information utile dans l'investigation de crimes liés aux armes à feu. Au cours du siècle dernier, de nombreuses approches ont été proposées. Les plus prometteuses se basent sur le suivi de la diminution au cours du temps des résidus de tir volatils dans l'espace de tête (et plus particulièrement, des composés les plus volatiles, tels que le naphtalène). Au regard des bons résultats obtenus dans des applications analogues (par exemple l'estimation du temps depuis la dernière décharge d'armes à feu et de cartouches de fusil), la solid phase micro-extraction (SPME) suivie par de la chromatographie en phase gazeuse a été récemment suggérée pour l'analyse des cartouches d'armes de poings tirées. Cependant, des résultats insatisfaisants ont été reportés, principalement en raison de limitations analytiques (problèmes de reproductibilité et de sensibilité), de la faible sélection de composés ciblés et du choix des modèles interprétatifs. Afin d'étudier davantage le potentiel de l'analyse de l'espace de tête pour estimer le temps depuis la décharge des cartouches d'armes de poing, une nouvelle approche a été développée dans le cadre de cette thèse de doctorat. Cette approche se fonde sur l'extraction des douilles par headspace sorptive extraction (HSSE), qui est une technique plus exhaustive (et donc, plus reproductible et sensible) que la SPME. Les composés cibles ont été choisis sur la base d'une étude préliminaire, et l'ensemble de la méthodologie analytique a ensuite été optimisée en utilisant une approche statistique multivariée basée sur la théorie des plans d'expérience. Les résultats ont montré de bonnes performances analytiques en termes de limites de détection et de répétabilité. Son application à des échantillons réels a révélé que les quantités de composés volatils diminuent rapidement dans les premières heures après la décharge (< 10 h), mais ils ne disparaissent pas totalement de l'espace de tête des douilles. Ainsi, en utilisant un modèle d'interprétation multivarié, il a été possible de fournir des estimations du temps depuis la décharge jusqu'à 48 h et de différencier des cartouches récemment tirées de celles âgées. A ce propos, les meilleures approches ont été une combinaison de normalisation par paires suivie d'une transformation logarithmique (i.e., pairwise log-ratios, PLR) et l'implémentation des paramètres de vieillissement ainsi obtenus dans des modèles random forests (RF) ou partial least squares (PLS). Les effets de plusieurs facteurs d'influence (par exemple la position de la cartouche, l'humidité et la température) ont été étudiés plus avant. Alors que tous affectaient d'une certaine manière la cinétique de vieillissement des composés, ils ne portaient pas atteinte à la précision de la datation des modèles multivariés, du moment qu'il n'y avait pas de différence significative entre le matériel indiciaire et celui de référence en question. Un modèle évaluatif a également été développé et a permis d'assigner un rapport de vraisemblance aux résultats analytiques considérant des hypothèses alternatives sur le temps depuis la décharge. Ainsi, les résultats ont permis de montrer que l'analyse en espace de tête peut effectivement fournir des preuves utiles pour aider les praticiens à répondre aux questions concernant le temps depuis la décharge d'une cartouche. Des recherches complémentaires restent nécessaires, mais les résultats sont prometteurs vers le développement d'une méthodologie complète de datation

Time since discharge of 9mm cartridges by headspace analysis, part 2: Ageing study and estimation of the time since discharge using multivariate regression.

Estimating the time since discharge of spent cartridges can be a valuable tool in the forensic investigation of firearm-related crimes. To reach this aim, it was previously proposed that the decrease of volatile organic compounds released during discharge is monitored over time using non-destructive headspace extraction techniques. While promising results were obtained for large-calibre cartridges (e.g., shotgun shells), handgun calibres yielded unsatisfying results. In addition to the natural complexity of the specimen itself, these can also be attributed to some selective choices in the methods development. Thus, the present series of papers aimed to systematically evaluate the potential of headspace analysis to estimate the time since discharge of cartridges through the use of more comprehensive analytical and interpretative techniques. Following the comprehensive optimisation and validation of an exhaustive headspace sorptive extraction (HSSE) method in the first part of this work, the present paper addresses the application of chemometric tools in order to systematically evaluate the potential of applying headspace analysis to estimate the time since discharge of 9mm Geco cartridges. Several multivariate regression and pre-treatment methods were tested and compared to univariate models based on non-linear regression. Random forests (RF) and partial least squares (PLS) proceeded by pairwise log-ratios normalisation (PLR) showed the best results, and allowed to estimate time since discharge up to 48h of ageing and to differentiate recently fired from older cartridges (e.g., less than 5h compared to more than 1-2 days). The proposed multivariate approaches showed significant improvement compared to univariate models. The effects of storage conditions were also tested and results demonstrated that temperature, humidity and cartridge position should be taken into account when estimating the time since discharge

Time since discharge of 9mm cartridges by headspace analysis, part 1: Comprehensive optimisation and validation of a headspace sorptive extraction (HSSE) method.

Estimating the time since discharge of spent cartridges can be a valuable tool in the forensic investigation of firearm-related crimes. To reach this aim, it was previously proposed that the decrease of volatile organic compounds released during discharge is monitored over time using non-destructive headspace extraction techniques. While promising results were obtained for large-calibre cartridges (e.g., shotgun shells), handgun calibres yielded unsatisfying results. In addition to the natural complexity of the specimen itself, these can also be attributed to some selective choices in the methods development. Thus, the present series of paper aimed to more systematically evaluate the potential of headspace analysis to estimate the time since discharge of cartridges through the use of more comprehensive analytical and interpretative techniques. Specifically, in this first part, a method based on headspace sorptive extraction (HSSE) was comprehensively optimised and validated, as the latter recently proved to be a more efficient alternative than previous approaches. For this purpose, 29 volatile organic compounds were preliminary selected on the basis of previous works. A multivariate statistical approach based on design of experiments (DOE) was used to optimise variables potentially involved in interaction effects. Introduction of deuterated analogues in sampling vials was also investigated as strategy to account for analytical variations. Analysis was carried out by selected ion mode, gas chromatography coupled to mass spectrometry (GC-MS). Results showed good chromatographic resolution as well as detection limits and peak area repeatability. Application to 9mm spent cartridges confirmed that the use of co-extracted internal standards allowed for improved reproducibility of the measured signals. The validated method will be applied in the second part of this work to estimate the time since discharge of 9mm spent cartridges using multivariate models

Estimating the time since discharge of spent cartridges: a logical approach fro interpreting the evidence

Estimating the time since discharge of a spent cartridge or a firearm can be useful in criminal situa-tions involving firearms. The analysis of volatile gunshot residue remaining after shooting using solid-phase microextraction (SPME) followed by gas chromatography (GC) was proposed to meet this objective. However, current interpretative models suffer from several conceptual drawbacks which render them inadequate to assess the evidential value of a given measurement. This paper aims to fill this gap by proposing a logical approach based on the assessment of likelihood ratios. A probabilistic model was thus developed and applied to a hypothetical scenario where alternative hy-potheses about the discharge time of a spent cartridge found on a crime scene were forwarded. In order to estimate the parameters required to implement this solution, a non-linear regression model was proposed and applied to real published data. The proposed approach proved to be a valuable method for interpreting aging-related data

Development of a novel headspace sorptive extraction method to study the aging of volatile compounds in spent handgun cartridges

Estimating the time since the last discharge of firearms and/or spent cartridges may be a useful piece of information in forensic firearm-related cases. The current approach consists of studying the diffusion of selected volatile organic compounds (such as naphthalene) released during the shooting using solid phase micro-extraction (SPME). However, this technique works poorly on handgun car-tridges because the extracted quantities quickly fall below the limit of detection. In order to find more effective solutions and further investigate the aging of organic gunshot residue after the discharge of handgun cartridges, an extensive study was carried out in this work using a novel approach based on high capacity headspace sorptive extraction (HSSE). By adopting this technique, for the first time 51 gunshot residue (GSR) volatile organic compounds could be simultaneously detected from fired handgun cartridge cases. Application to aged specimens showed that many of those compounds presented significant and complementary aging profiles. Compound-to-compound ratios were also tested and proved to be beneficial both in reducing the variability of the aging curves and in enlarging the time window useful in a forensic casework perspective. The obtained results were thus particularly promising for the development of a new complete forensic dating methodology

From: Larry Roberts (enclosure)

Illegal trafficking of pharmaceutical products by criminal organisations is a global threat for public health. Drugs for erectile dysfunction such as phosphodiesterase type 5 inhibitors are the most commonly counterfeited medicines in Europe. The search of possible toxic chemical substances in seized products is needed to provide early warning for public health. Furthermore, the elemental profile of the seized products can be useful in criminal investigations. For the first time an ion beam analysis (IBA) procedure to characterise authentic Viagra® tablets and sildenafil-based illegal products is described. Moreover, results are compared with the ones obtained by instrumental neutron activation analysis (INAA) on authentic Viagra® tablets in two reactors. IBA results showed that a combination of particle-induced X-ray emission (PIXE) and secondary ion mass spectrometry using primary ions with energies in the range of several MeV (MeV-SIMS) is a powerful tool to characterise different products in a straightforward manner, allowing discrimination between legal and illegal products. INAA allowed accurate elemental quantification and also showed a great potential for the future implementation of an inter- laboratory classification system

Development of European standards for evaluative reporting in forensic science : The gap between intentions and perceptions

Criminal justice authorities of EU countries currently engage in dialogue and action to build a common area of justice and to help increase the mutual trust in judicial systems across Europe. This includes, for example, the strengthening of procedural safeguards for citizens in criminal proceedings by promoting principles such as equality of arms. Improving the smooth functioning of judicial processes is also pursued by works of expert working groups in the field of forensic science, such as the working parties under the auspices of the European Network of Forensic Science Institutes (ENFSI). This network aims to share knowledge, exchange experiences and come to mutual agreements in matters concerning forensic science practice, among them the interpretation of results of forensic examinations. For example, through its Monopoly Programmes (financially supported by the European Commission), ENFSI has funded a series of projects that come under the general theme ‘Strengthening the Evaluation of Forensic Results across Europe’. Although these initiatives reflect a strong commitment to mutual understanding on general principles of forensic interpretation, the development of standards for evaluation and reporting, including roadmaps for implementation within the ENFSI community, are fraught with conceptual and practical hurdles. In particular, experience through consultations with forensic science practitioners shows that there is a considerable gap between the intentions of a harmonised view on principles of forensic interpretation and the way in which works towards such common understanding are perceived in the community. In this paper, we will review and discuss several recurrently raised concerns. We acknowledge practical constraints such as limited resources for training and education, but we shall also argue that addressing topics in forensic interpretation now is of vital importance because forensic science continues to be challenged by proactive participants in the legal process that tend to become more demanding and less forgiving

Differentiation of blue ballpoint pen by positive and negative mode LDI-MS

Usually, the differentiation of inks on questioned documents is carried out by optical methods and thin layer chromatography (TLC). Therefore, spectrometric methods were also proposed in forensic literature for the analysis of dyes. Between these techniques, laser desorption/ionization mass spectrometry (LDI-MS) has demonstrated a great versatility thanks to its sensitivity to blue ballpoint ink dyes and minimal sample destruction. Previous researches concentrated mostly on the LDI-MS positive mode and have shown that this analytical tool offers higher discrimination power than high performance TLC (HPTLC) for the differentiation of blue ballpoint inks. Although LDI-MS negative mode has already been applied in numerous forensic domains like the studies of works of art, automotive paints or rollerball pens, its potential for the discrimination of ballpoint pens was never studied before. The aim of the present paper is therefore to evaluate its potential for the discrimination of blue ballpoint inks. After optimization of the method, ink entries from 33 blue ballpoint pens were analyzed directly on paper in both positive and negative modes by LDI-MS. Several cationic and anionic ink components were identified in inks; therefore, pens were classified and compared according to their formulations. Results show that additional information provided by anionic dyes and pigments significantly increases the discrimination power of positive mode. In fact, it was demonstrated that classifications obtained by the two modes were, to some extent, complementary (i.e., inks with specific cationic dyes not necessarily contained the same anionic components)

Probabilistic graphical models to deal with age estimation of living persons

Due to the rise of criminal, civil and administrative judicial situations involving people lacking valid identity documents, age estimation of living persons has become an important operational procedure for numerous forensic and medicolegal services worldwide. The chronological age of a given person is generally estimated from the observed degree of maturity of some selected physical attributes by means of statistical methods. However, their application in the forensic framework suffers from some conceptual and practical drawbacks, as recently claimed in the specialised literature. The aim of this paper is therefore to offer an alternative solution for overcoming these limits, by reiterating the utility of a probabilistic Bayesian approach for age estimation. This approach allows one to deal in a transparent way with the uncertainty surrounding the age estimation process and to produce all the relevant information in the form of posterior probability distribution about the chronological age of the person under investigation. Furthermore, this probability distribution can also be used for evaluating in a coherent way the possibility that the examined individual is younger or older than a given legal age threshold having a particular legal interest. The main novelty introduced by this work is the development of a probabilistic graphical model, i.e. a Bayesian network, for dealing with the problem at hand. The use of this kind of probabilistic tool can significantly facilitate the application of the proposed methodology: examples are presented based on data related to the ossification status of the medial clavicular epiphysis. The reliability and the advantages of this probabilistic tool are presented and discussed