Soilwater Conductivity Analysis to Date and Locate Clandestine Graves of Homicide Victims

In homicide investigations, it is critically important that postmortem interval and postburial interval (PBI) of buried victims are determined accurately. However, clandestine graves can be difficult to locate; and the detection rates for a variety of search methods (ranging from simple ground probing through to remote imaging and near‐surface geophysics) can be very low. In this study, simulated graves of homicide victims were emplaced in three sites with contrasting soil types, bedrock, and depositional environments. The long‐term monthly in situ monitoring of grave soil water revealed rapid increases in conductivity up to 2 years after burial, with the longest study evidencing declining values to background levels after 4.25 years. Results were corrected for site temperatures and rainfall to produce generic models of fluid conductivity as a function of time. The research suggests soilwater conductivity can give reliable PBI estimates for clandestine burials and therefore be used as a grave detection method.     

Geophysical Monitoring of Simulated Clandestine Graves Using Electrical and Ground‐Penetrating Radar Methods: 0–3 Years After Burial*,†

Abstract: This study provides forensic search teams with systematic geophysical monitoring data over simulated clandestine graves for comparison to active cases. Simulated “wrapped” and “naked” burials were created. Multigeophysical surveys were collected over a 3‐year monitoring period. Bulk ground resistivity, electrical resistivity imaging, multifrequency ground‐penetrating radar (GPR), and grave and background “soil‐water” conductivity data were collected. Resistivity surveys revealed the naked burial had consistently low‐resistivity anomalies, whereas the wrapped burial had small, varying high‐resistivity anomalies. GPR 110‐ to 900‐MHz frequency surveys showed the wrapped burial could be detected throughout, with the “naked” burial mostly resolved. Two hundred and twenty‐five megahertz frequency GPR data were optimal. “Soil‐water” analyses showed rapidly increasing (year 1), slowly increasing (year 2), and decreasing (year 3) conductivity values. Results suggest resistivity and GPR surveys should be collected if target “wrapping” is unknown, with winter to spring surveys optimal. Resistivity surveys should be collected in clay‐rich soils.     

The suitability of using domestic pigs (Sus spp.) as human proxies in the geophysical detection of clandestine graves

Research in many forensic science fields commonly uses domestic pigs (Sus spp.) as proxies for human remains, due to their physiological and anatomical similarities, as well as being more readily available. Unfortunately, previous research, especially that which compares the decompositional process, has shown that pigs are not appropriate proxies for humans. To date, there has not been any published research that specifically addresses whether domestic pigs are adequate human proxies for the geophysical detection of clandestine graves. As such, the aim of this paper was to compare the geophysical responses of pig cadavers and human donor graves, in order to determine if pigs can indeed be used as adequate human proxies. To accomplish this, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) responses on single and multiple pig cadaver graves were compared to single and multiple human donor graves, all of which are in known locations within the same geological environment. The results showed that under field conditions, both GPR and ERT were successful at observing human and pig burials, with no obvious differences between the detected geophysical responses. The results also showed that there were no differences in the geophysical responses of those who were clothed and unclothed. The similarity of the responses may reflect that the geophysical techniques can detect graves despite what their contents are. The study implications suggest that experimental studies in other soil and climate conditions can be easily replicated, benefiting law enforcement with missing persons cases.     

Time-lapse geophysical investigations over a simulated urban clandestine grave

A simulated clandestine shallow grave was created within a heterogeneous, made-ground, urban environment where a clothed, plastic resin, human skeleton, animal products, and physiological saline were placed in anatomically correct positions and re-covered to ground level. A series of repeat (time-lapse), near-surface geophysical surveys were undertaken: (1) prior to burial (to act as control), (2) 1 month, and (3) 3 months post-burial. A range of different geophysical techniques was employed including: bulk ground resistivity and conductivity, fluxgate gradiometry and high-frequency ground penetrating radar (GPR), soil magnetic susceptibility, electrical resistivity tomography (ERT), and self potential (SP). Bulk ground resistivity and SP proved optimal for initial grave location whilst ERT profiles and GPR horizontal "time-slices" showed the best spatial resolutions. Research suggests that in complex urban made-ground environments, initial resistivity surveys be collected before GPR and ERT follow-up surveys are collected over the identified geophysical anomalies.     

Utilizing a magnetic locator to search for buried firearms and miscellaneous weapons at a controlled research site

Forensic personnel generally use basic all-metal detectors for weapon searches because of their ease of use and cost efficiency. For ferromagnetic targets, an alternative easy to use and low-cost geophysical tool is a magnetic locator. The following study was designed to demonstrate the effectiveness of a common, commercially available magnetic locator in forensic weapon searches by determining the maximum depth of detection for 32 metallic forensic targets and testing the effects of metallic composition on detection. Maximum depth of detection was determined for 16 decommissioned street-level firearms, six pieces of assorted scrap metals, and 10 blunt or bladed weapons by burying each target at 5-cm intervals until the weapons were no longer detected. As expected, only ferromagnetic items were detected; weapons containing both ferromagnetic and nonferromagnetic components were generally detected to shallower depths. Overall, the magnetic locator can be a useful addition to weapon searches involving buried ferromagnetic weapons.     

Geoforensic search to crime scene: Remote sensing,geophysics, and dogs

In the absence of surface indications of burial sites, law enforcement or humanitarian organizations are faced with the difficult task of focusing large-scale ground searches to a manageable excavation area. A geoforensic-based survey may exclude parts of the landscape for reasons such as diggability or viewshed analysis but leave areas still too large for invasive exploration. This work examines how drone-based remote sensing, geophysics, and search dogs may be combined to narrow such searches. Here, we ask the reader to consider two examples where forensic geomorphology and land use provided a range of possible burial locations. Following this is a multi-proxy approach to similar dilemma, with a search-to-scene case study using remote sensing (drone photography), geophysics, ground probes, and search dogs. This approach is not presented as a definitive guide, but serves as an example of the conjunctive use of well-studied methods to approach a common problem in geoforensics.     

Long‐term Geophysical Monitoring of Simulated Clandestine Graves using Electrical and Ground Penetrating Radar Methods: 4–6 Years After Burial

This ongoing monitoring study provides forensic search teams with systematic geophysical data over simulated clandestine graves for comparison to active cases. Simulated “wrapped,” “naked,” and “control” burials were created. Multiple geophysical surveys were collected over 6 years, here showing data from 4 to 6 years after burial. Electrical resistivity (twin electrode and ERI), multifrequency GPR, grave and background soil water were collected. Resistivity surveys revealed that the naked burial had low‐resistivity anomalies up to year four but then difficult to image, whereas the wrapped burial had consistent large high‐resistivity anomalies. GPR 110‐ to 900‐MHz frequency surveys showed that the wrapped burial could be detected throughout, but the naked burial was either not detectable or poorly resolved. 225‐MHz frequency GPR data were optimal. Soil water analyses showed decreasing (years 4 to 5) to background (year 6) conductivity values. Results suggest both resistivity and GPR surveying if burial style unknown, with winter to spring surveys optimal and increasingly important as time increases.