RESUMO

Soils have distinctive chemical, physical, mineralogical and biological properties, which make it possible to differentiate them in different environments and also to test for an association of a particular questioned item with a crime scene. Mineral compositions and structures in the soil clay fraction can reflect a distinct characteristic when analyzed by powerful techniques. In this way, the aim of this study was to compare the discriminative power of Fe-oxides concentrated clay samples from the same soil class with and without differences in parent material when analyzed using the Rietveld method and two sources of X-ray diffraction: conventional and high-resolution synchrotron radiations. Clay samples were Fe concentrated (kaolinite and gibbsite removal) to clarify mineralogical composition of 12 samples from three simulated crime scenes, developed under claystone and granite. By Rietveld refinement, detailed crystallographic data were obtained to discriminate samples according their provenance. By synchrotron radiation, mineral data demonstrated the power of quantitative (crystallite size and minerals contents) and qualitative (identification of majoritarian and accessory minerals) analysis by Rietveld refinement, which provides well-resolved data able to discriminate samples from different and same geology. The techniques can be applied in other criminal investigations given their potential of discrimination.

Assuntos

Óxidos , Síncrotrons , Argila , Análise dos Mínimos Quadrados , Minerais/análise , Óxidos/análise , Solo/química , Difração de Raios X

RESUMO

Soil trace evidence can be useful in criminal investigations. A homicide which had occurred in South Brazil been concluded through the courts with a guilty conviction. A spade with soil traces adhering to it was seized from the confessed killer's house, it having been established that it had been used to bury parts of the victim's body. In the context of this confession, it provided an opportunity to test a protocol of analysis and verify the potential of discriminate soil sample analysis in such case works. This allowed us to test the practice of sequential analysis which had been developed for forensic case works in Brazil, with three sequential extractions: (i) 0.2 mol/L pH 3.0 ammonium oxalate; (ii) dithionite-citrate-bicarbonate; and (iii) 0.5 mol/L NaOH. It was possible to predict the sequence of events related to the homicide by using the sequential extraction technique and to conclude that: (i) the A horizon soil from the burial location of the torso was found to be very similar to the soil samples which had been recovered from the spade, which was able to be established despite there only being a small amount of soil adhering to the spade; (ii) the location where the legs were buried contributed a low amount of soil adhering to the spade. Therefore, it is suggested that, where possible, sequential extractions should be prioritized from a questioned sample to best provide information about the likely sequence of contact places and this test likely scenarios and criminal events.