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 last discharge of firearms and spent ammunition elements: state of the art and perspectives

The estimation of the time since last discharge of firearms or spent ammunition elements (e.g., casings) may provide crucial information in the investigation of a shooting incident and, eventually, the following trial. Herein, an exhaustive review of the methods described in the literature is reported, with the aim to evaluate their potential and limitations from a forensic perspective. This work, in particular, highlighted the fact that a number of investigations have been carried out in the field during the last century (with an especially high rate in the last 30 years), but the implementation of related procedures in forensic laboratories is still rare. The situation has been discussed and a series of propositions have been forwarded, in order to overcome challenges and facilitate the implementation of dating approaches in real casework

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 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

Challenge outcome and conclusion

In the following we report on the outcome of the ICWE 2015 Rapid Mashup Challenge (RMC), describe the voting system used, and draw some conclusions regarding the presented works

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

Plant Poisons in the Garden: A Human Risk Assessment

A study of the plants, and their associated poisons, in the Poison Garden at The Alnwick Garden was undertaken across a calendar year. By selecting 25 plants in the Poison Garden, we have been able to develop a single chromatographic method for the determination and quantification of 15 plant toxins by liquid chromatography mass spectrometry (LC-MS). Chromatographic separation was achieved on a C18 column (3.5 µm, 100 × 4.6 mm) with a gradient method using water +0.1 formic acid and methanol +0.1 formic acid. The developed method was validated for precision, linearity, limits of detection and quantification and extraction recoveries. The method showed good linearity with a R2 value of >0.995 for all 15 compounds with good precision of 10.7, 6.7 and 0.3 for the low, medium and high calibration points, respectively. The LC-MS method was used to analyse 25 plant species, as well as their respective parts (i.e., bulb, flower, fruit, leaf, pollen, seed, stem and root), to assess the human risk assessment to children (aged 1 to <2 years) in relation to the plant toxin and its respective LD50. The analysis found that the greatest potential health risks were due to the ingestion of Colchicum autumnale and Atropa belladonna. As a caution, all identified plants should be handled with care with additional precautionary steps to ensure nil contact by children because of the potential likelihood of hand-to-mouth ingestion

A study on contactless airborne transfer of textile fibres between different garments in small compact semi-enclosed spaces

Interpretation of fibre evidence at activity level requires extensive knowledge of all the possible transfer mechanisms that may explain the presence of fibres on a recipient surface of interest. Herein, we investigate a transfer method that has been largely understudied in previous literature: contactless transfer between garments through airborne travel. Volunteers were asked to wear UV-luminescent garments composed of different textile materials and situate themselves in a semi-enclosed space (elevator) for a pre-determined period of time with other participants, who wore non-luminescent recipient garments. The latter were then inspected for fibres using UV-luminescent photographic techniques. Results showed that contactless transfer between garments is possible. Indeed, a number of fibres were observed after most of the experiments. As many as 66 and 38 fibres were observed in the experiments involving cotton and polyester donor garments, compared to 2 and 1 fibres in those involving acrylic and wool donor garments, respectively. In this regard, the type of donor garment was found to be a significant factor. Multifactorial ANOVA supported these observations (p < 0.001) and further indicated a statistically significant influence of elevator door opening/closing (p < 0.001), people entering/exiting (p = 0.078) and the recipient garment (p = 0.030). Therefore, contactless transfer of fibres between garments can occur and can do so in (ostensibly) high numbers. This should be taken into consideration when interpreting fibre evidence at activity level and may have a major implication for the assignment of evidential values in some specific cases