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Myra Hindley, Fred West and this last year Andrew Pountley, have all come to have something in common. A specialist scientific search technique has been employed to bring them to justice and their victims to rest – the technique is forensic geophysics.
Forensic geophysics is ‘the study of locating and mapping hidden objects or features that are underground or underwater’ (Dupras, 2006). Geophysical methods have the potential to aid the location and recovery of human remains as they can, non-invasively, very rapidly survey extensive areas where a suspected clandestine burial has taken place. Subsequent targeted anomalies could then be investigated using conventional intrusive methods. Early successes in the 1990s, particularly the Fred West case, raised the profile of forensic geophysics, particularly Ground Penetrating Radar (GPR), but to-date, geophysics has only been used sporadically and with varied success. There is a significant gap in knowledge of the best methods for collection, analysis and interpretation of geophysical data for forensic applications. It should be noted that as long as there is a geophysical contrast between a ‘target’ and the background materials, then other items could be resolved (see Milsom, 2003), such as buried weapons, money caches and even evidence of human occupation or excavation, but this article concentrates on clandestine burial searches.
Collaborative researchers from Keele University (led by Dr Jamie Pringle, a geoscientist), Staffordshire University (led by Dr John Cassella, a forensic scientist) and STATS Geophysical Ltd. (led by Dr George Tuckwell, a geophysicist) have been conducting field trials in the Midlands over simulated (mock) shallow burials to determine the best, near-surface, geophysical detection technique(s) and if these change over time after burial. Obviously every suspected burial will be unique, for example, different soil types and environmental conditions, depth below ground level, etc. We have therefore been attempting to characterize our surveyed sites for local geology, soil type determination and moisture content, potential surface objects (fences, utility services etc.) etc. to partially overcome this. We would recommend doing this prior to deciding on a geophysical survey of a suspected area; this may show that it would be unsuitable. The time since burial has been shown to have a big effect on the geophysical response (see figure on right). From our research on the Midlands urban test sites, we have shown that bulk ground electrical methods, particularly resistivity, is the most promising technique to rapidly survey a suspected area and pinpoint a burial.
We would then recommend that higher-resolution, comparatively slower to acquire geophysical surveys, e.g. collecting 2D GPR or Electrical Resistivity Tomography (ERT) vertical section profiles. These should then be undertaken to further resolve the detail of the burial. This resolution should be able to determine the burial depth, the ‘target’ size, any other buried material and perhaps the ‘target’s’ likely condition. [See Pringle et al., (2008) for more detail]. By repeatedly surveying the simulated clandestine graves over time, we have also found that there are significant differences in the geophysical responses obtained, depending upon such factors as the time of year, soil moisture content and the estimated time since burial. Geophysical surveys over suspected burials in summer often detect secondary decomposition products as well as the ‘target’ but winter surveys also show surprisingly good results. We would recommend that GPR surveys should be undertaken if a burial is less than a month old; bulk ground electrical surveys show good results after this time period (see figure on left). By sequentially sampling decomposition products of pig cadavers in simulated burials, we have found that fluid conductivity linearly increases with time, which may explain the resistivity results.
We have been developing robust geophysical data acquisition and processing protocols to provide the best possible chance of detecting a clandestine burial using near-surface geophysical methods. Examples of this include suspected areas should be geophysically surveyed one-way on parallel, survey lines on a grid pattern, ideally in a south-north orientation. Most survey areas have natural trends from low to high areas, that reflect local geology or other material variation that should be removed from the data to clearly image a ‘target’. This is called a site trend, and should be removed from most datasets. Careful GPR data acquisition should include constant trace spacing on parallel, closely-spaced, survey lines. GPR data processing should include topographic correction and generation of ‘time-slices’ for maximum chance of imaging ‘targets’.
Ultimately, forensic geophysics has the potential to develop into a standard technique to assist the police service in both the rapid detection & characterisation of clandestine shallow burials.
For further information or advice, please contact Dr Jamie Pringle, School of Physical Sciences & Geography, Keele University, Staffs, ST5 5BG or email: firstname.lastname@example.org The Forensic Search Advisory Group provide technical expertise and support in the location and recovery of UK buried or hidden remains and have a 24 hour pager service.
Dupras, D., Schultz, J., Wheeler, S. & Williamns, L. 2006. Forensic Recovery of Human Remains: Archaeological Approaches. Taylor & Francis Group Publishers, Boca Raton, Florida, USA, 232pp.
Jervis, J., Pringle, J.K., Cassella, J.P. & Tuckwell, G.T. (in press). Using soil and groundwater data to understand resistance surveys over a simulated clandestine grave. In: Proceedings of the 2nd International Soils Forensics Conference, Edinburgh, UK, 30th October to 1st November 2007.
Milsom, J. 2003. Field geophysics. Geological Field Guide Series, 3rd Edition, Wiley, Chichester, UK, 244pp.
Pringle, J.K., Jervis, R., Cassella, J.P. & Cassidy, N.J. 2008. Time-lapse geophysical investigations over a simulated urban clandestine grave. Journal of Forensic Sciences, in press.