Particle size analysis of soils under simulated scene of crime conditions: the interest of multivariate analyses

Two simulated scenes of crime have been studied. Soil traces adhering to boots, sport shoes and tissues have been compared with control samples using particle size analysis. Comparisons of percentage of particles per class interval and multivariate analyses were used to determine how the size distribution of each suspect sample varied compared to the original distribution. A loss of coarse fractions characterized most of the suspect samples even though they were derived from soils having different distributional patterns. However, the differences between control and suspect samples were found to be more important for soils dominated by extreme size classes than for soils rich in medium size particles. The differences among soil samples from the same source were found to be restricted to the extreme size classes. The finding of significant differences within size classes ranging from 1 to 0.063 mm should be then considered as a dissimilarity sign between trace sample and hypothetic control soil.     

The evaluation of methods for soil analysis under simulated scenes of crime conditions

Five simulated scenes of crime have been studied in which the soils adhering to shoes, car tyres and plant roots have been compared with multiple control samples using dry colour, ashed colour, pH, saccharide levels and particle size analysis. Colour and pH were found to be as reproducible under simulated scenes of crime conditions as for true duplicates from homogeneous soil, whereas the variation in saccharide levels was slightly greater than for true duplicates. The interpretational scheme developed for the silt and sand fractions of homogeneous soils was applied to the samples from each simulated scene of crime and every comparison was found to be similar at the 99% confidence limit.     

Particle size analysis of sediments, soils and related particulate materials for forensic purposes using laser granulometry

Particle size is a fundamental property of any sediment, soil or dust deposit which can provide important clues to nature and provenance. For forensic work, the particle size distribution of sometimes very small samples requires precise determination using a rapid and reliable method with a high resolution. The Coulter trade mark LS230 laser granulometer offers rapid and accurate sizing of particles in the range 0.04-2000 microm for a variety of sample types, including soils, unconsolidated sediments, dusts, powders and other particulate materials. Reliable results are possible for sample weights of just 50 mg. Discrimination between samples is performed on the basis of the shape of the particle size curves and statistical measures of the size distributions. In routine forensic work laser granulometry data can rarely be used in isolation and should be considered in combination with results from other techniques to reach an overall conclusion.     

A comparative study of gunshot residue originating from 9 mm Luger ammunition from various producers

Following previous work on differentiation between gunshot residue according to the type of ammunition used, a specific investigation was undertaken of traces originating from 9 mm Luger ammunition using SEM-EDX. The aim of this study was to determine whether GSR originating from this type of ammunition is similar, or whether differentiation could be made between particular manufacturers of Luger ammunition. The results were collected in the form of counts of particles in each of seven key elemental classes being combinations of lead, antimony and barium. These were then adjusted to a factor known as frequency of occurrence which allows comparison of the distribution of particles within the classes between samples with differences in absolute particle counts. The relationships between the samples were examined using non-parametric statistical tests: R-Spearman and tau-Kendall rank correlation coefficients. It has been found that most of the studied samples of GSR were similar to each other despite their originating from various manufacturers.     

Can analysis of a small clod of soil help to solve a murder case?

Soil forensics utilizes extensive soil information to answer legal questions and test hypotheses. The main difficulty often is the determination of different variables from a small amount of soil sample collected on the suspect. We developed a sequential mineralogical and chemical analyses to assess a limited quantity of soil vestiges (0.5 g) from a suspect's vehicle (adhered to the outside rear-view mirror and to the left front fender) involved in a murder case and compared them with the surface samples found at the victim's body disposal site at the Graciosa Road, Paraná State, Brazil. All results affirm that the suspect’s vehicle could have been in contact with the edge of the Graciosa Road, approximately the place where the victim’s body was located. As a result of the soil analysis and comparison, the results support the likely contact of the suspect’s vehicle with the crime scene.     

Screening of soil evidence by a combination of simple techniques: validity of particle size distribution.

The validity of the determination of particle size distribution for forensic soil identification was studied using 73 soil samples collected from a 20 km x 15 km area. Soil particles were first divided into two fractions by wet sieving with a sieve with a 0.05 mm aperture size. Dry sieving was used to analyze the coarse particle fraction and a particle size analyzer was used for the fine particle fraction. The number of particle size classes measured by sieving could be reduced to three, <0.05, 0.05-0.2, and 0.2-2 mm, which enabled 87.9% of the soil samples to be discriminated. Measurements made with the particle size analyzer on the fine particle fraction increased the discriminating power to 95.9%. The use of particle size analysis by sieving in combination with color examination allowed us to discriminate 99.5% of the soil samples, even when particle size analysis of the fine particle fraction was not carried out.     

Quantitative analysis of sharp-force trauma: an application of scanning electron microscopy in forensic anthropology.

Scanning electron microscopy (SEM) has occasionally been used by anthropologists and forensic scientists to look at morphological characteristics that certain implements leave on bone. However, few studies have addressed techniques or protocols for assessing quantitative differences between tool marks on bone made by different bladed implements. In this study, the statistical variation in cut mark width was examined between control and test samples on bone using a scalpel blade, paring knife, and kitchen utility knife. Statistically significant differences (p < .0005) were found between cut marks made by the same knife under control and test conditions for all three knife types used in the study. When the control sample and test samples were examined individually for differences in mean variation between knife types, significant differences were also found (p < .0005). While significant differences in cut mark width were found, caution should be used in trying to classify individual cut marks as being inflicted by a particular implement, due to the overlap in cut mark width that exists between different knife types. When combined, both quantitative and qualitative analyses of cut marks should prove to be more useful in trying to identify a suspect weapon. Furthermore, the application of SEM can be particularly useful for assessing many of these features.     

Pollen on grass clippings: putting the suspect at the scene of the crime.

In a case of alleged sexual assault, the pollen content of samples of grass clippings and soil from the suspect's clothing and shoes was compared to that of a sample of grass clippings from the alleged crime scene (a grassy area) to determine whether or not the suspect had been at the scene. The clothing and shoe samples showed a very strong correlation with each other and with the sample from the alleged crime scene in the combination of the different types of pollen present, very strongly supporting the contention that the suspect had been at the scene.     

The combined use of pollen and soil analyses in a search and subsequent murder investigation

This case report shows how soil analyses (particularly petrology) can be used in conjunction with pollen in order to refine or strengthen an association. Soil samples from a car believed to have been used by the suspect in a missing persons case was subjected to soil and pollen analyses. The soil characteristics and petrology were used to redefine the search area using geology and soils maps, the pollen and vegetative remains were used to target woodlands with a particular species mix. As a result two bodies were located and the environmental evidence was used in the subsequent trial. In this case the history of the vehicle was well known and the wheel arches and footwells provided reliable soil traps. The advantage of combining the techniques is that soil evidence (both mineralogy and other inclusions) provides a geological/soils match while the pollen provides independent evidence of vegetation type providing a combination that may be rare or unique.     

The forensic analysis of soil organic by FTIR

In order to elucidate the discriminating power of various soil analytical techniques, over 100 soils samples were analyzed using conventional analysis (i.e., color, percent organic and density gradient) and a novel FTIR technique. The FTIR technique involves collecting a spectrum of a soil sample that has been oxidatively pyrolysed, and therefore all organic have been degraded. This spectrum is subtracted from the spectrum of the same sample that contained the organic prior to pyrolysis. This resultant IR spectrum represents the organic portion of the sample. The use of organic components increases the discrimination in soils that are otherwise similar. We have illustrated the usefulness of this technique by selecting four soil samples, which have identical Munsel color values but can be discriminated by subtractive ETIR. We propose that the ETIR spectra of the organic portion of soil serves a useful purpose in forensic investigations.     

Multi-technique comparison of source and primary transfer soil samples: an experimental investigation.

The comparison of soil samples is of long-standing and increasing interest in forensic science. Routine comparisons should involve the use of several techniques in combination. A wide range of analytical techniques can be used, choice being dependent on several factors including sample size and character, time constraints and cost limitations. In this paper results are presented for experiments carried out to test the effectiveness of four of the available analytical techniques (spectro-photometric colour determination, laser diffraction particle size analysis, stable isotope analysis and chemical element analysis) used to compare single source and primary transfer soil samples. Four soil types and five footwear types were used. All four techniques showed excellent precision and good resolving power between soil types. Only relatively small differences were obtained between source and transferred soil samples in terms of colour, stable carbon and nitrogen isotope ratios and elemental chemistry. Slight but significant differences were found in grain size, indicating that the primary transfer process is to some extent grain size selective.     

Bacterial Profiling of Soil For Forensic Investigations: Consideration of Ex Situ Changes in Questioned and Known Soil Samples

Soil, being diverse and ubiquitous, can potentially link a suspect or victim to a crime scene. Recently scientists have examined the microbial makeup of soil for determining its origin, and differentiating soil samples is well-established. However, when soil is transferred to evidence its microbial makeup may change over time, leading to false exclusions. In this research, “known” soils from diverse habitats were stored under controlled conditions, while evidence soils were aged on mock evidence. Limited quantities of soil were also assayed. Bacterial profiles were produced using next-generation sequencing of the 16S rRNA gene. Overall, known soils stored open at room temperature were more similar to evidence soils over time than were known soils stored bagged and/or frozen. Evidence soils, even as little as 1 mg, associated with the correct habitat 99% of the time, accentuating the importance of considering ex situ microbial changes in soil for its successful use as forensic evidence.     

Identification and comparison of electrical tapes using instrumental and statistical techniques: I. Microscopic surface texture and elemental composition

Comparisons of polyvinyl chloride electrical tape typically rely upon evaluating class characteristics such as physical dimensions, surface texture, and chemical composition. Given the various techniques that are available for this purpose, a comprehensive study has been undertaken to establish an optimal analytical scheme for electrical tape comparisons. Of equal importance is the development of a quantitative means for sample discrimination. In this study, 67 rolls of black electrical tape representing 34 different nominal brands were analyzed via scanning electron microscopy and energy dispersive spectroscopy. Differences in surface roughness, calendering marks, and filler particle size were readily apparent, including between some rolls of the same nominal brand. The relative amounts of magnesium, aluminum, silicon, sulfur, lead, chlorine, antimony, calcium, titanium, and zinc varied greatly between brands and, in some cases, could be linked to the year of manufacture. For the first time, quantitative differentiation of electrical tapes was achieved through multivariate statistical techniques, with 36 classes identified within the sample population. A single-blind study was also completed where questioned tape samples were correctly associated with known exemplars. Finally, two case studies are presented where tape recovered from an improvised explosive device is compared with tape recovered from a suspect.     

Distribution of gunshot residues--the influence of weapon type

Gunshot residue (GSR) analysis is a frequently used forensic method for investigating shooting events. In this process, GSR-particles are detected on pertinent objects, often the hands of a suspect, with energy dispersive X-ray microanalysis in a scanning electron microscope. The question asked in court is usually the following: "… has or has not a given shot been fired by the suspect (at a certain place and time)?" Unfortunately, this question frequently cannot be answered by the analyst. Only the presence or absence of "characteristic" GSR-particles on the investigated sample can be stated with confidence. All other assumptions are inherently biased by many factors that are usually only known by the culprit or are generally unknown. In order to draw more profound conclusions from GSR analytical results, the dynamics of GSR particles have to be considered, i.e., how these particles reach a suspect. Consequently, the formation of the plume after firing was investigated for eleven different firearms with high speed-video analysis. The results show that a vast scope exists between revolvers - distributing many particles near the shooter - and e.g. shotguns that are quite sealed. These differences between the various weapon types should be considered for interpretation of the results of GSR-analysis.     

Potential of soil organic matter molecular chemistry determined by pyrolysis-gas chromatography/mass spectrometry for forensic investigations

Wetlands near urban centers may be more isolated areas and can be chosen for the disposal of bodies or used as a crime scene. The predominant soils in these areas usually have a high content of organic matter (OM), classified as Histosols. Soil organic matter (SOM) is composed of many different compounds that can be identified by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The study aimed to use Py-GC/MS to classify small amounts of organic soil in a forensic context. We sampled Histosols from five representative sites of Curitiba, Brazil. The molecular composition of the samples was determined by byPy-GC/MS. The factor analysis was carried out, and the factor scores showed a clear differentiation between the sites. Compounds indicative of relatively fresh plant material was separated from more recalcitrant and charred material. Py-GC/MS has the potential to be a useful tool to study the composition of SOM in Histosols to track the trace sample collected from a crime suspect.     

High‐throughput Sequencing of Trace Quantities of Soil Provides Reproducible and Discriminative Fungal DNA Profiles

High‐throughput sequencing (HTS) offers improved resolution between forensic soil samples by characterizing individual taxa present; however, the heterogeneous distribution of taxa in soils, and limited quantity of material available, may hinder the reliability of HTS in casework. Using HTS of the internal transcribed spacer, we examined the effect of soil mass (50, 150, and 250 mg) on fungal DNA profiles, focusing on reproducibility and discriminatory power between close proximity soils, and samples with similar textural classification. The results show that reduced soil mass had no significant effect on sample differentiation and that 150 mg soil provides the most reproducible DNA profiles across different soil types. In addition, Ascomycota was identified as a robust fungal target for forensic intelligence as this phylum was detected consistently across all samples regardless of sample quantity. Overall, this study highlights the value of trace quantities of soil for use in forensic casework.     

Discrimination of Soils at Regional and Local Levels Using Bacterial and Fungal T‐RFLP Profiling*

Abstract: DNA profiling of microbial communities has been proposed as a tool for forensic comparison of soils, but its potential to discriminate between soils from similar land use and/or geographic location has been largely unexplored. We tested the ability of terminal restriction fragment length polymorphism (T‐RFLP) to discriminate between soils from 10 sites within the Greater Wellington region, New Zealand, based on their bacterial and fungal DNA profiles. Significant differences in bacterial and fungal communities between soils collected from all but one pair of sites were demonstrated. In some instances, specific terminal restriction fragments were associated with particular sites. Patch discrimination was evident within several sites, which could prove useful for site‐specific matching (e.g., matching shoe/car tire print to an object). These results support the need for further understanding of the spatial distribution of soil microbial communities before DNA profiling of soil microbial communities can be applied to the forensic context.     

Assessing the potential of bacterial DNA profiling for forensic soil comparisons

A pilot study was undertaken to evaluate DNA profiling of the bacterial community in soil as an alternative to geological methods for forensic soil comparisons. Soil samples from three different ecosystems were compared, and the variation within and between ecologically different sites was determined by using terminal restriction fragment (TRF) analysis of 16S ribosomal DNA. Comparison of TRF profiles revealed that samples from within a specific ecosystem (e.g., a field) showed a significantly higher similarity to each other than to those from another ecosystem (e.g., a forest). In addition, some profile features were unique to specific ecosystems. These features may allow the determination of characteristic profiles that will facilitate identification of ecologically different sites, so that a given sample collected from a suspect could be identified as originating from, for example, a field, rather than a forest. The implications of these preliminary findings for forensic investigations are discussed.     

Soil forensics: How far can soil clay analysis distinguish between soil vestiges?

Soil traces are useful as forensic evidences because they frequently adhere to individuals and objects associated with crimes and can place or discard a suspect at/from a crime scene. Soil is a mixture of organic and inorganic components and among them soil clay contains signatures that make it reliable as forensic evidence. In this study, we hypothesized that soils can be forensically distinguished through the analysis of their clay fraction alone, and that samples of the same soil type can be consistently distinguished according to the distance they were collected from each other. To test these hypotheses 16 Oxisol samples were collected at distances of between 2 m and 1.000 m, and 16 Inceptisol samples were collected at distances of between 2 m and 300 m from each other. Clay fractions were extracted from soil samples and analyzed for hyperspectral color reflectance (HSI), X-ray diffraction crystallographic (XRD), and for contents of iron oxides, kaolinite and gibbsite. The dataset was submitted to multivariate analysis and results were from 65% to 100% effective to distinguish between samples from the two soil types. Both soil types could be consistently distinguished for forensic purposes according to the distance that samples were collected from each other: 1000 m for Oxisol and 10 m for Inceptisol. Clay color and XRD analysis were the most effective techniques to distinguish clay samples, and Inceptisol samples were more easily distinguished than Oxisol samples. Soil forensics seems a promising field for soil scientists as soil clay can be useful as forensic evidence by using routine analytical techniques from soil science.