Locating concealed homicide victims: Developing the role of geoforensics

Abstract

Historically police searches for homicide victims' graves have been undertaken by the use of large numbers of police, military and public volunteers, conducting visual or manual probe line searches covering formalised gridded sectored areas. Speculative digging of large areas of ground has also been employed with variable success. Mineral exploration geologists, engineering geologists and geohazards specialists traditionally investigate the ground using a range of methods and techniques. Before such ground investigations are undertaken, a conceptual geological model of the ground is developed. This provides information on, for example: tectonic setting, stratigraphy, lithology, structure, hydrogeology, hydrology, groundwater, hydrochemistry, superficial deposits, principal soil types, depth to bedrock, nature of bedrock interface, engineering and physical properties of the ground, geomorphological processes, mining, past land use, current land use, geological hazards and man's influences. In a similar way, the properties of a buried or concealed body may also be determined and how in particular these have influenced the geology. This provides estimates of the target's age, size, and geometry, expected depth of burial, time and duration of burial, state of preservation or decomposition, physical, chemical, hydrogeological and geotechnical variations compared to the surrounding ground. An understating of the undisturbed (pre-burial) and disturbed (post-burial) geology and the target (body and associated objects) properties are crucial before the correct search strategy and choice of instrumentation may be decided, and the optimum method of deployment identified. These may include geophysics, geochemistry, satellite imagery, air photo interpretation and invasive methods (such as auguring, drilling, trial pitting and trenching). Geological investigative techniques are applicable to law enforcement searches, since the underlying search philosophy, concepts and principles are similar. That is, there is a buried/ concealed 'object' or 'target' desirable to be found. The most important services a geologist can give the police and a law enforcement search strategist are: the production of a geological model of a potential grave site, an understanding of the geological and geomorphological processes, the characterisation and understanding of the origin, source and properties of the soils, rocks and target (body), and a choice of detecting methods. For the geologist (and other subject matter experts) to be effectively incorporated into a search team, he/she must be an effective communicator of complex geological (scientific) terminology, recognise the limitations of his/ her skills and capabilities and be aware of the boundaries and interface with other subject matter forensic experts. The principal objective of this chapter is to describe the effective and efficient processes to locate concealed victims of homicide. It also seeks to show how the combined skills and expertise of law enforcement and geoforensic search specialists enable the ground in the vicinity of homicide graves to be better understood and more professionally searched.