Soil vestiges might provide information about a crime scene. The Rietveld method with X-ray diffraction data (RM-XRD) is a nondestructive technique that makes it possible to characterize minerals present in the soils. Soil clays from the metropolitan region of Curitiba (Brazil) were submitted to DCB treatment and analyzed using XRD with CuK a radiation in the step-scan mode (0.02°2h/5 s). The GSAS+EXP-GUI software was used for RM refinement. The RM-XRD results, together with the principal component analysis (PCA) (52.6% total variance), showed the kaolinite predominance in most analyzed samples and the highest quartz contents in "site 1." Higher anatase, and gibbsite and muscovite contents influenced discrimination, mainly in "site 3" and "site 1," respectively. These results were enough to discriminate clays of four sites and two horizons using a reduced amount of sample showing that the technique can be applied to the investigation into soil vestiges.

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Soils are a complex mixture with a variety of mineralogical, chemical, biological and physical properties, which can be explored within forensic case work. This study aimed to apply energy-dispersive X-ray fluorescence (EDXRF) and Fourier transform infrared (FTIR) spectroscopic techniques to discriminate soil samples collected in southern Brazil in a forensic context. Four replicates of soil were collected at four sites: two sites from the same parent material (claystone) and two other sites from limestone and granite/gneiss respectively. The physical and chemical (organic and mineral composition) and spectroscopic techniques (EDXRF and FTIR) produced 16 quantitative variables from only 2 g of sample. The main results from a forensic context were the separation of the soils collected from close neighbourhoods developed on the same parent material and the separation of soils collected in the A and B horizons of the same soil profile. The highest degree of similarity in the clustering of samples collected at the same site was 98.6% (B horizon in claystone domain). In addition to the parent material, the effect of organic matter on the chemical and mineralogical characteristics of the A horizon was important in the grouping dynamics of samples. This work demonstrated the potential of spectroscopic techniques in a forensic context.

Soil traces can be used as evidence in criminal investigations due their transferability, great variability and persistence. The soil samples originated from a crime scene that occurred in the Curitiba Metropolitan Region, Brazil. Physical, chemical and mineralogical analyses were carried out on the soil samples. All results were statistically analysed using multivariate analysis (PCA) to verify the relative positioning of soil traces which had been recovered from a stolen safety deposit box (SDB) from a vehicle suspected of being used in the SDB transportation, and from the site allegedly used in the opening of the SDB. The methods employed were effective in discriminating between the sampling sites. The soil from the site used in the opening of the SDB could be excluded as being the location where the soil transferred to the SDB had originated as it was different in many characteristics.Supplementary material: The organic matter content of the samples, and their gibbsite and kaolinite values obtained by thermogravimety analysis (S1), and X-ray diffraction patterns of the silt + clay fractions (S2) are available at https://doi.org/10.6084/m9.figshare.c.4561004

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