Dark Side: In the Field

 

Surface change such as vegetation acceleration or retardation as a consequence of ground disturbance can be seen from the air using conventional aerial photography; even single graves can be identified in some circumstances. Photographs are preferably taken at an oblique angle during clear weather when the sun is low in the sky (i.e., winter months, or summer mornings or evenings). Vegetation stress due to the proximity of decaying cadaver(s) can be seen using infrared photography, and heat emitted as a consequence of either insect infestation or putrefaction and autolysis can be detected using aerial thermal imagery, as can heat differentials between disturbed and undisturbed soils. Baseline data from which to observe more recent change can also be obtained by comparing pre-existing aerial photographs in any of the forms mentioned above (vertical or oblique, traditional, infra-red, or multispectral imagery), with those recently taken. In the U.K., complete coverage of air-photographs have a fine enough degree of detail to indicate archaeological features. Taking photographs of an area subsequent to its becoming an area of search and comparing such information with preexisting but preferably recent (i.e., no more than five years) coverage can be immensely useful in highlighting areas of change or disturbance. Equally as important as aerial photographs is prior knowledge of previous land use and the location of services. The position and date of installation of water and gas mains, electricity and television cables, septic tanks, and soak-aways are essential. In areas of settlement it is important to know the date of the construction of such garden features as ponds, patios, extensions to buildings, and outbuildings. Patios are, in my own experience, a favored medium under which to dispose of victims, as are soak-aways.

The use of line-searches by police officers causes the forensic archaeologist considerable consternation, as such an approach can be potentially catastrophic, damaging surface indicators of disturbance. The typical police response of digging what appear to be randomly sited holes in a search area can be even more damaging, and unless they are exceptionally lucky will have no greater chance of success than of finding a needle in haystack. However, a minimalist but carefully considered and informed search by experienced archaeologists can be invaluable in detecting evidence of soil disturbance or vegetation change indicative of the numerous impacts of a burial on plant regimes. When examining a particular search area for topographical and vegetation anomalies it is imperative to have a basic understanding of geology, the soil sciences, and the affects of such processes as colluvium and alluviation on the landscape. The experienced eye can differentiate between natural soil. change and changes that are anthropogenic in origin. Similarly, an understanding of the impact of soil types and different hydrological regimes on taphonomic processes is crucial to be able to predict the condition of any surviving human remains14 and associated materials, such as clothing. It is also essential to have some knowledge of the local flora and the effects of disturbance, changes in pH, nutrient enrichment, increased moisture retention, and changed water-levels. The burial of a decaying body will effect all of these processes at different times and to a different extent in the decomposition process, hence an understanding of taphonomic change is crucial.16 Such change will be moderated or enhanced by such variables as pre-deposition insect infestation, depth of burial, cause of death, previous health and weight of the victim, toxicology, and presence and nature of clothing or body coverings. The burial of a victim can cause overlying vegetation to be stressed, to die, to be accelerated, or simply to be anomalous in terms of normal plant succession in the area. It can also disturb a dormant seed bank and result in the colonization of plant species not presently visible locally. A recently excavated experimental grave (containing a Soay sheep) on the chalk downland in Dorset provides a useful example. The grave was clearly demarked by the almost exclusive colonization of a member of the Compositae (daisy) family, which though common in the area before intensive farming took over, is now only rarely seen but known to like disturbed ground. Similar species exist for most soil types, and it behooves the archaeologist to either have an awareness of them or to involve a botanist. A burial in an area of acid grassland has the potential to encourage the success of plant species tolerant of alkaline conditions after a period of months following burial, reflecting proteolysis.

Field searches can involve a trained cadaver dog, and in the U.K. such animals are used in conjunction with ground probes which are believed to release gases associated with decomposition. In the U.S., most dogs are airscent only. In both cases, the success of this method is very much dependant on the temperature and humidity being moderate, not extreme, and on wind strength and direction. Dogs can form a useful part of a multi-pronged approach to cadaver detection.

Resistivity survey measures the electrical resistance of the buried soil. An electric current is passed between two probes pushed a few centimeters into the ground surface. This is undertaken within a measured grid and the results plotted within the defined area. Resistance is affected by the moisture content of the soil, which is altered in areas of below-ground disturbance. Variation of the probe separation allows an estimation of size and depth of anomalies. Resistivity is less effective on waterlogged soils than free-draining ones, and is unlikely to give useful results in heavily disturbed soils. Soil disturbance not only alters moisture retention levels locally, but will also cause local anomalies in the magnetic field. Magnetometry can be used to detect such change. This method involves no probing and is also carried out within a grid. Magnetometry will also pick up evidence of buried ferrous metals which might be associated with a burial. It is less effective than resistivity in urban contexts where building materials include fired clay products, fragments of which may be in the garden soils. It is adversely affected by steel pipes, metal fences, and other ferrous debris, and is not effective in heavily disturbed sites.

Alternative approaches can be adopted where more traditional search and location methods cannot be applied. Augers, or ground probes, that remove samples of the buried soil can be useful in criminal investigations. Different types of augers are used for different soil types. When the author was asked some 15 years previously by the police to assess, as discretely as possible, whether a victim was buried in one of a series of legitimate graves in a group of cemeteries, the above methods could not be employed. As the depth of the legitimate burials was known by the cemetery authorities and made available to us, augering was used to assess the grave fill down to the depth of the original burial. This method was successful in locating a body. It took only minutes to examine each grave, and was inexpensive and unobtrusive in a sensitive setting. Augers can also be used as a survey tool and auger transects undertaken as a search method. Clearly, augers are not affective in stony soils and gravels, but in experienced hands can be very effective tools. When, for various reasons, none of the above methods can be used on a site where there is every reason to believe a grave may be concealed, a last resort is to strip off the vegetation and top soil using plant machinery equipped with a wide toothless bucket. On smaller areas, such stripping could be done by hand. A colleague and I have used machine stripping successfully in a mass grave location in the Balkans where the perpetrators dumped spoil to a depth of up to one meter over the entire search area and littered it with waste metal. This method can be fast and effective, a good machine operator being the principle requirement. Once the overburden of topsoil and vegetation n is removed, the archaeologist can examine the exposed surface for evidence of grave cuts through the natural undisturbed substrate. Anomalous features can then be quickly examined to see if they are of interest to the inquiry. In some substrates grave-cuts are likely to become ill-defined due to hydrological conductivity (e.g., alluvial deposits in flood planes or sands), excessive root or rodent disturbance, or because the substrate is already very disturbed. While the former two criteria are unlikely to happen within a forensic framework in such cases narrow evaluation trenches can also be cut systematically and strategically across the site to ensure that nothing is missed. Evaluation trenches are not advisable when seeking individual graves but can be useful when attempting to locate mass burials.

The fundamental principle underlying archaeological excavation and recording is that the digging of a grave will cause discontinuity in the medium into which it is cut and that it will itself conform to the laws of stratigraphy. Consequently, the approach to excavation is a destructive process and must be sequential and thoroughly recorded to allow the evidence to be reconstructed and interpreted for the courts. In order to accurately record the stratigraphy of a grave and the location of any materials within that stratigraphic context, archaeologists excavate the fill of a grave in spits, or layers of five or ten centimeters, depending on the circumstances of each case. Each layer is retained in a sealed sterile container for further analysis and individually numbered. It is imperative to be able to say which layer any materials found within a grave came from, as this could be crucial in successfully linking a perpetrator to the site. Generally, a forensic grave will be excavated in two halves so that a section of the fill showing clearly any layers or differences can be accurately recorded. The fill will be removed this way until the top of the cadaver or skeleton is exposed.

A major difference between archaeological and forensic graves is that in forensic cases, unless the grave, is very shallow, a trench will be dug around one or two sides of the grave, allowing the grave walls to be removed. This enables the victim to be more easily recovered than from above. This method does preclude close scrutiny of the removed grave walls in deep graves, and evidence of tool marks and possibly flakes of paint from tools may be lost as a consequence. Unlike in archaeological graves, in forensic cases, whether cadavers or skeletons, the remains are not scrupulously cleaned in situ, as this may remove crucial forensic evidence. Enough of the body will be revealed to record its position and its relationship to any other objects or materials recovered. The body or skeleton will then be removed by methods appropriate to the particular circumstances.

Ideally, as many appropriate methods as possible are used and the results from each are compared and contrasted, compiling a series of “hot-spots” for further evaluation. What such methods detect are below-surface anomalies which may reflect a burial but can also reflect natural and other anthropogenic activities.

Acknowledgements:

 

www.politie.nl  Politiekorpschef  @Janny Knol©

 

www.aived.nl    AIVD – @Erik Akerboom ©

 

www.politie.nl WEB Politie - @Henk van Essen©

 

https://www.police-nationale.interieur.gouv.fr/ @ Stephane Folcher ©

 

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