Perpetrators of fatal crimes will on occasion attempt to conceal their wrongdoings by burying the evidence – that is, attempting to bury human cadavers. This can be problematic during a forensic investigation for a number of reasons. Firstly, the search for a victim’s body may well be relatively blind, with investigators having little or no idea as to where a body has been buried. In some instances, a body may well be so damaged or decomposed that little recognisable human remains are present. The perpetrator may later remove the body from the burial site, perhaps fearing discovery, leaving behind no obvious trace that a body was ever buried there.
So what can investigators do to determine if an area of soil was the site of a clandestine grave (illicit burial site)? A number of methods that have been developed to tackle this question.
Certain chemical compounds may be indicative of decomposing flesh. Sterols have been suggested as a potential biomarker for decomposition fluids – that is, the presence of them in soil could indicate whether or not a body has decomposed in that location, depending on the types of sterols present and in what amounts. Sterols are a class of organic compound, of which cholesterol is perhaps the most well-known sterol present in animal cells. This compound can be found in plants too, but in a significantly smaller amount, thus the unexpected presence of cholesterol in soil will typically indicate some kind of animal-related activity. Research examining the decomposition fluids in soils found sterols to be beneficial in this application (Von der Luhe et al, 2013). A number of pig carcasses were buried over a few months, with soil samples being collected from underneath the cadavers at different time points after burial. Cholesterol and coprostanol were detected in the soil, and it is these substances that were of particular interest to the researchers. Coprostanol is formed via hydrogenation of cholesterol in the intestinal tract of higher mammals, thus it is considered a useful biomarker associated with the faecal matter of animals such as humans and pigs. The concentration of these compounds was greater during the time period in which the pigs were undergoing the putrefaction stage of decomposition, at which point fluids would be leeching into the soil. This suggests a certain time frame in which these compounds are useful as indicators of decomposition fluids.
Cholesterol
The research suggested that, as the cadaver decomposes, decomposition fluids leak into the soil, depositing cholesterol and coprostanol (and a whole range of other substances). Thus the presence of these compounds in a particular area of soil, particularly if nearby similar areas did not contain them, could indicate previous decomposition of a human (or equally a pig or other animal) in the area. However it is vital to note that these compounds could equally be detected in the soil as a result of faecal matter, though potentially in considerably lower concentrations than those produced by a whole decomposing body.
Other compounds resulting from decomposition are of equal interest in detecting potential gravesites. Adipocere, also known as grave wax, is an insoluble, white substance known to form if a body decomposes in very specific conditions. The presence of this substance in soil can of course indicate the decomposition of a body, but how does one distinguish between the decomposition fluids of a human and those of another mammal? Research has aimed to answer this question using isotopes (Bull et al, 2009). By focusing on the ratio of 13C to 12C content of particular fatty acids from the fats of various animals, it was suggested that it is possible to distinguish between adipose fats from humans and those from other animals, such as pigs, though further work may be required to develop this application.
Other researchers are applying existing forensic techniques in a novel manner to the detection of clandestine graves. When the body decomposes, a significant amount of nitrogen is released, typically in the form of ammonium and nitrate (Hopkins et al, 2000). Ninhydrin, a compound already readily available to law enforcement due to its use as a method of fingerprint development, can produce a blue or purple pigment upon reaction with certain nitrogen-containing compounds.
Ninhydrin is typically used for visualising fingerprints (http://daten.didaktikchemie.uni-bayreuth.de)
One particular study examining ninhydrin reactive nitrogen (Carter at al, 2008) left a number of mammalian cadavers to decay over a period of a month, after which soil samples from the burial sites were collected and analysed for ninhydrin reactive nitrogen. This work discovered that cadaver burial resulted in the concentration of NRN in the soil approximately doubling, thus concluding that it may be possible to use ninhydrin as a presumptive test for gravesoil. Of course this particular method is somewhat limited by the fact that any mammalian cadaver (and plants or faeces for that matter) will most likely produce this increase in nitrogen-containing compounds which will react with ninhydrin, but an interesting application of an existing indicator nonetheless.
The various methods of using the chemical analysis of soil to detect clandestine graves are plentiful and fascinating. Despite the limitations, namely the possibility of animal faeces and non-human decomposition providing false positive results, these techniques may at the very least act as a kind of presumptive or complimentary test for possible burial sites.
References
Von der Luhe, B. Dawson, L. A. Mayes, R. W. Forbes, S. L. Fiedler, S. Investigation of sterols as potential biomarkers for the detection of pig (S. s. domesticus) decomposition fluid in soils. Forensic Sci Int. 230 (2013), pp. 68-73.
Bull, I. D. Berstan, R. Vass, A. Evershed, R. P. Identification of a disinterred grave by molecular and stable isotope analysis. Sci Justice. 49 (2009), pp. 142-149.
Carter, D. O. Yellowless, D. Tibbett, M. Using ninhydrin to detect gravesoil. J Forensic Sci. 53 (2008), pp. 397-400.
Locard's Lab 