Detection of gasoline on suspects' hands: study of different sampling alternatives

Arsonists may use ignitable liquids to start, accelerate and amplify fires. The sampling of volatiles present on the hands of suspected arsonists is therefore sometimes carried out in the course of the investigation of (possible) deliberate fires. Several collection protocols have been proposed, relying on the concentration of volatiles by the transfer on PVC gloves and further passive headspace extraction with Activated Charcoal Strips (ACS). Previous research findings assessing the use of Activated Carbon Cloth (ACC) – initially developed for the adsorption of gas in military applications – opens the path to new perspectives regarding the extraction and the concentration of ignitable liquid residues in general, and for the sampling on hands in particular. Five alternative methods (four relying on the use of ACC and one on ACS) were considered for the collection of gasoline traces present on the hands and their subsequent analysis by gas chromatography – mass spectrometry. Gasoline was deposited onto the palms of volunteers to study the differences between the collection method using ACS and those using ACC. For the latter, either the volunteer hands were placed in nylon bags with an ACC on the palm or suspended, or, powder-free latex gloves were used, with an ACC on the palm or in a separate extraction, with the glove in a nylon bag and the ACC suspended. The results showed that the background contamination was not distinguishable between ACS and ACC and their sampling ability was comparable. The two methods relying on the deposition of ACC directly on the surface of the palm where gasoline was deposited showed significantly higher collection capacity than other methods, provided that the ACC was in direct contact with the contaminated zone. The results showed that three main factors affected the collection of gasoline on the hands: the distance between the skin and the sorbent (ACC or ACS) in case of direct concentration of volatiles on the sorbent, the exposure time, and the space between the hand and the glove or bag (i.e. the headspace volume). This research opens new perspectives for the sampling of ignitable liquid residues through the use of ACC. It corroborates the perceived potential of ACC for the extraction and concentration of volatile compounds, particularly for fire debris analysis purposes. While the experiments were focused on the collection of gasoline on hands, the results provide valuable information in a more general way for the sampling of fire debris

δ 15N measurement of organic and inorganic substances by EA-IRMS: a speciation-dependent procedure

Little attention has been paid so far to the influence of the chemical nature of the substance when measuring δ 15N by elemental analysis (EA)-isotope ratio mass spectrometry (IRMS). Although the bulk nitrogen isotope analysis of organic material is not to be questioned, literature from different disciplines using IRMS provides hints that the quantitative conversion of nitrate into nitrogen presents difficulties. We observed abnormal series of δ 15N values of laboratory standards and nitrates. These unexpected results were shown to be related to the tailing of the nitrogen peak of nitrate-containing compounds. A series of experiments were set up to investigate the cause of this phenomenon, using ammonium nitrate (NH4NO3) and potassium nitrate (KNO3) samples, two organic laboratory standards as well as the international secondary reference materials IAEA-N1, IAEA-N2—two ammonium sulphates [(NH4)2SO4]—and IAEA-NO-3, a potassium nitrate. In experiment 1, we used graphite and vanadium pentoxide (V2O5) as additives to observe if they could enhance the decomposition (combustion) of nitrates. In experiment 2, we tested another elemental analyser configuration including an additional section of reduced copper in order to see whether or not the tailing could originate from an incomplete reduction process. Finally, we modified several parameters of the method and observed their influence on the peak shape, δ 15N value and nitrogen content in weight percent of nitrogen of the target substances. We found the best results using mere thermal decomposition in helium, under exclusion of any oxygen. We show that the analytical procedure used for organic samples should not be used for nitrates because of their different chemical nature. We present the best performance given one set of sample introduction parameters for the analysis of nitrates, as well as for the ammonium sulphate IAEA-N1 and IAEA-N2 reference materials. We discuss these results considering the thermochemistry of the substances and the analytical technique itself. The results emphasise the difference in chemical nature of inorganic and organic samples, which necessarily involves distinct thermochemistry when analysed by EA-IRMS. Therefore, they should not be processed using the same analytical procedure. This clearly impacts on the way international secondary reference materials should be used for the calibration of organic laboratory standards. Figure Control chart of the δ 15N value of IAEA-N1, IAEA-NO-3 and NH4NO3 analysed a) with oxygen injection (analytical cycle 70 s, oxygen for 60 s, sample start and stop at 18 s/20 s), b) with oxygen injection (analytical cycle 70 s, oxygen for 60 s, sample start and stop at 0 s/2 s and 5 s/7 s), c) without oxygen injection (analytical cycle 70 s, sample start and stop at 18 s/20 s

Study of chemical modifications in acidified ignitable liquids analysed by GC-MS

In this work, mixtures of gasoline with sulphuric acid and diesel fuel with sulphuric acid were analysed by gas chromatography&-mass spectrometry (GC&-MS). The results showed considerable qualitative and semi-quantitative modifications in the chromatographic profiles of the ignitable liquids (ILs). In the case of acidified gasoline, the alteration of the abundances of aromatic compounds and the hydrolysis of an oxygenated compound such as methyl tert-butyl ether (MTBE), in addition to the immediate and unexpected appearance of tert-butylated compounds were observed. In the case of acidified diesel fuel, the alteration of aromatic compounds occurred. These sequential changes were then studied in detail in order to explain the chemical modifications taking place. These extensive chemical modifications may be considered as a new chromatographic profile distortion effect, the acidification of ILs. As such modifications are not generally taken into account in the criteria followed to assess the classification of an IL, we propose some recommendations helping to the identification of acidified ILs. This information can be especially useful to detect and identify non-burned ILs from seized or failed improvised incendiary devices made with mixtures of sulphuric acid&-IL, or ILs altered intentionally with the aim to modify their composition

Effects of chemical warfare agent decontaminants on trace survival: Impact on fingermarks deposited on glass

Following a chemical incident involving chemical warfare agents or more broadly, chemical weapons, there are two possible approaches in dealing with the traditional forensic analysis of contaminated exhibits. The first is to analyze the contaminated items under safe conditions (i.e. in laboratories dedicated to the handling of such substances), while the second relies on item decontamination prior to processing them in traditional forensic laboratories. One of the main limitations of the latter is the possible degradation or destruction of traces caused by the decontamination process. Hence, it is crucial to have as much information as possible on the impact of different decontamination agents and procedures on traces. This research presents experimental results on the recovery of fingermarks on glass after the application of decontaminants typically used in case of chemical incidents. The impact of 11 decontaminants on fingermarks deposited on glass and on the subsequent enhancement with cyanoacrylate and Small Particle Reagent (SPR) was evaluated (by visual examination) by four evaluators. The results of the study demonstrated that the persistence of fingermarks on glass is highly dependent on the type of decontaminant used. Decontamination agents based on the principle of nucleophilic substitution to neutralize toxic chemicals allowed good subsequent development of fingermarks with SPR. Powdered decontaminants did not show any indication of alteration of fingermarks, whereas decontamination with oxidants leads to variable results

Étude sur l'impact d'un délai d'effacement automatique pour les profils ADN de personnes prévenues

Depuis plus de 30 ans, les traces ADN contribuent significativement aux investigations criminelles, grâce notamment à la mise en place de banques de données génétiques. Si leur utilité est amplement reconnue, certains aspects – comme la durée de conservation du profil des individus – continuent à alimenter les débats, de par les implications en matière d’atteinte au droit de la personne. En Suisse, la durée de rétention dépend de l’issue de la procédure judiciaire, ce qui complexifie la procédure d’effacement. La définition d’un délai d’effacement automatique constituerait donc une solution intéressante pour simplifier la procédure, tout en garantissant l’efficacité de la trace ADN et le droit à l’oubli. Cette étude vise donc à déterminer s’il est possible de supprimer le profil ADN d’un individu de la banque de données sans que cela nuise à l’élucidation d’enquêtes futures et, le cas échéant, de proposer un délai d’effacement automatique le plus opportun. À la suite des résultats de l’étude de Girardet (2014) sur l’application des délais d’effacement en Suisse, trois échéances – 5, 8 et 10 ans – ont été retenues dans la présente étude. Issu de la banque de données ADN suisse, l’échantillon utilisé comprenait les données sur les prélèvements ADN réalisés (N = 106 346) et sur les traces biologiques identifiées (N = 16 516) entre 2005 et 2014 dans quatre cantons suisses. Les résultats obtenus montrent que l’effacement des profils n’affecte pas l’identification des traces. En effet, 80 % des identifications surviennent dans l’année qui suit l’enregistrement du profil génétique du prévenu, le solde étant identifié dans un délai de 10 ans au plus. Quant aux infractions dont les traces ont été identifiées au-delà d’un délai de 5 ans (N = 313), ou de 8 ans (N = 36), il apparaît que la grande majorité de ces affaires ont trait à des infractions contre le patrimoine, même si on relève également quelques cas d’atteinte à la personne. Ainsi, en se fondant sur le jeu de données mises à disposition, les résultats de cette étude montrent qu’un délai automatique de 10 ans assurerait à satisfaction l’efficacité de l’exploitation de la banque de données, tout en respectant la proportionnalité de la pratique.DNA traces have made a significant contribution to criminal investigations for over 30 years, especially after the creation of DNA databases. Although the effectiveness of these databases is widely recognized, some issues – such as the retention period for DNA profiles – are still widely discussed because of the potential threat they pose to people’s fundamental rights and freedoms. In Switzerland, the length DNA is retained is determined through legal proceedings, which makes any decision to delete more complicated. Defining a time after which deletion would be automatic would simplify the removal procedure while both recognizing the usefulness of DNA in investigations and guaranteeing that it will not be retained indefinitely. This study looks at whether it is possible to delete a DNA profile from the database without affecting future investigations and proposes the most suitable delay before automatic deletion. Following the results of the study of Girardet (2014), delays of 5, 8, and 10 years were considered. Our sample, based on data in Switzerland’s national DNA database collected between 2005 and 2014 in four Swiss cantons, consisted of information on DNA samples from arrestees (N = 106 346) as well as identified biological traces (N = 16 516). Results show that removal of DNA profiles does not affect identification of the traces. In fact, 80 % of identifications occur in the year following the entry of an arrestee’s DNA profile, while the 20 % remaining are identified in a maximum of 10 years. In cases where identification of the traces required longer than 5 years (N = 313) or 8 years (N = 36), the offenses were almost all property crimes, although a few violent crimes were also observed. Based on the data available, automatic deletion after 10 years would ensure the efficiency of DNA database while respecting the proportionality of measure.Desde hace más de 30 años, los rastros de ADN contribuyen significativamente a las investigaciones criminales, gracias, sobre todo, al establecimiento de bases de datos genéticas. Si bien su utilidad es ampliamente reconocida, algunos aspectos, como la duración de la conservación del perfil de los individuos, continúan alimentando los debates por las implicaciones en materia de derechos humanos. En Suiza, la duración de la retención depende del resultado del proceso judicial, lo que hace complejo el procedimiento de supresión. La definición de un retraso de supresión automático constituiría entonces una opción interesante para simplificar el procedimiento, garantizando la eficacidad del rastro de ADN y el derecho al olvido. Este estudio identifica si es posible suprimir un perfil de ADN de la base de datos sin que esto perjudique la elucidación de futuras encuestas y, en su caso, proponer un tiempo lo más oportuno posible de supresión automática. Siguiendo los resultados de un estudio (Girardet, 2014), tres plazos, de 5, 8 y 10 años, fueron considerados en el estudio. Proveniente de la base de datos suiza, la muestra utilizada incluía los datos sobre las muestras de ADN (N = 106 346) et sobre los rastros identificados (N = 16 516) entre el 2005 et el 2014 en cuatro cantones suizos. Los resultados obtenidos muestran que la supresión de los perfiles no afecta a la identificación de los rastros. En efecto, el 80 % de las identificaciones ocurren en el año siguiente al registro del perfil genético del acusado, el saldo estando identificado en un tiempo de 10 años o más. En cuanto a las infracciones cuyos rastros fueron identificados en un tiempo de más de 5 años (N = 313), o de 8 años (N = 36), parece que la gran mayoría de estos asuntos tienen que ver con infracciones contra el patrimonio, incluso si uno nota igualmente algunos casos de daño a la persona. Así, fundándose en el juego de datos disponible, los resultados de este estudio muestran que un tiempo automático de 10 años aseguraría satisfactoriamente la eficacidad de la explotación de una base de datos, respetando la proporcionalidad de la práctica

Forensic intelligence on illicit markets: the example of watch counterfeiting

Counterfeit luxury fashion goods have rarely been the subject of scientific studies. Very little is known about the mechanisms of this illicit market despite the apparent prevalence and their adverse consequences. Counterfeit watches remain one of the preferred targets in the luxury goods segment. The study of marks or traces in a forensic intelligence perspective can contribute to an improved understanding of the phenomenon. The aim of our research was to highlight different types of links that can be drawn between specimens of counterfeit watches, to carry out a thorough study of the information conveyed by the revealed links, to study their complementarity and to get an understanding of the intelligence that can be produced from these pieces of information. Thirty-five counterfeit watches of a commonly counterfeit watch brand including seven popular models were studied in this research. Chemical and physical links were found that corroborated existing knowledge and also revealed new connections between different seizures or specimens. The comparison of chemical and physical features combined with spatiotemporal information on the seized watches enabled us to produce intelligence disclosing possible aspects of the structure and the organisation of production and distribution channels. We were able to reveal or confirm links between watches that were previously unknown or uncertain and demonstrated the interconnection of all watches on a chemical and/or physical level, suggesting an overhead organised network with substructures. Despite the limited set of specimens that was considered, this study illustrates that forensic intelligence on this illicit market can be used to support consistent decision-making from all the key-players involved in the anti-counterfeiting process

How to recognize the traces left on a crime scene by a 3D-printed Liberator?: Part 1. Discharge, exterior ballistic and wounding potential

The Liberator is a firearm that can be manufactured from its blueprints, using a 3D-printer. This weapon made of nineteen pieces – eighteen in printed plastic and one metallic nail – raises questions such as its ability to fire a round, its wounding potential and the traces produced by its discharge. In particular, knowledge must be gained to infer that a 3D-printed handgun was used, reconstruct the shooting event involving such handgun, and gather information related to the type of 3D-printed handgun used. This study focused on the traces that could orientate forensic investigations when the use of a 3D-printed Liberator is suspected. In a first step, the Liberator was investigated to study its behaviour during the discharge and characterize traces produced by the discharge. To fulfil this goal, some Liberators were printed and assembled. Six Liberators fired a round. The discharge of the weapons was done under specific conditions allowing to collect ballistics data and traces produced by the shooting. The results showed that the barrel tended to break between the ignition of the primer and the moment the projectile exited the muzzle. The speed of the projectiles reached 140 m/s when the barrel broke, while it was about 170 m/s when barrel remained intact. The trajectory of the projectiles was sometimes disrupted, and the projectile tumbled on itself. It was thus very difficult to characterize the trajectory. The cavity wound caused by the fastest bullet was typical of a handgun wound firing a FMJ projectile (penetration of 21 cm in ballistics soap). On the other hand, the cavity caused by the slowest bullet was more representative of a splinter wound (penetration of 14 cm in ballistics soap). The study of gunshot residues collected on adhesive targets showed the presence of unburnt particles and small perforations caused by polymer pieces that concentrated around the entry holes

Recognition in Ants: Social Origin Matters

The ability of group members to discriminate against foreigners is a keystone in the evolution of sociality. In social insects, colony social structure (number of queens) is generally thought to influence abilities of resident workers to discriminate between nestmates and non-nestmates. However, whether social origin of introduced individuals has an effect on their acceptance in conspecific colonies remains poorly explored. Using egg-acceptance bioassays, we tested the influence of social origin of queen-laid eggs on their acceptance by foreign workers in the ant Formica selysi. We showed that workers from both single- and multiple-queen colonies discriminated against foreign eggs from single-queen colonies, whereas they surprisingly accepted foreign eggs from multiple-queen colonies. Chemical analyses then demonstrated that social origins of eggs and workers could be discriminated on the basis of their chemical profiles, a signal generally involved in nestmate discrimination. These findings provide the first evidence in social insects that social origins of eggs interfere with nestmate discrimination and are encoded by chemical signatures