Forensic Bulldozer as a Clandestine Grave Search Tool
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October 2009 - Volume 11 - Number 4 |
The Forensic Bulldozer as a Clandestine Grave Search Tool
Angi M. Christensen
Physical Scientist
Forensic Anthropology Program
Trace Evidence Unit
FBI Laboratory
Quantico, Virginia
W. Michael Lowe
Special Agent
Federal Bureau of Investigation
Little Rock, Arkansas
Gary W. Reinecke
Supervisory Special Agent
Evidence Response Team Unit
FBI Laboratory
Quantico, Virginia
Abstract | Introduction | Initial Search | The Forensic Bulldozer Approach | Discussion and Conclusions | Acknowledgments | References
This technical note describes the use of a bulldozer to attempt to locate a clandestine grave. The case involves a search area of approximately 2.5 acres where a body had been buried nine years earlier, as recalled to the best of witnesses’ memories. Traditional detection techniques were employed but unsuccessful, and witnesses were unable to be more specific about the possible grave location. Because of the amount of horizontal surface to be searched, bulldozers rather than backhoes were used, but in an innovative way. Although not often recommended for locating clandestine graves, the “trench and shift” bulldozer method represents an effective strategy for a large grave search area. No grave or body was located in this search, but several other small anomalies and items were discovered, and investigators felt confident that the area could be excluded as the location of the remains.
The topics of clandestine grave detection and recovery are well covered in the anthropological and archaeological literature (e.g., Dupras et al. 2006; France et al. 1992; Killam 1990; Ubelaker 1989). All authors and practitioners agree that meticulous methods using nondestructive or minimally destructive search techniques and small, hand-held tools for detection and recovery represent the ideal approach. Most recognize, however, that in certain circumstances it may be necessary to employ more extensive and potentially destructive methods when trying to locate a clandestine grave, and these methods often involve the use of heavy construction equipment to locate and excavate a burial site (Condon and Egan 1984; Hawley et al. 1994; Schiel and Gore 2006; Wedel 1951). A backhoe is often the equipment of choice because its blade can scrape away topsoil without having to drive over the search area, and it can still remove a large amount of soil in a relatively short period of time.
This article describes the use of a bulldozer in an attempt to locate a clandestine burial. Although some experts have specifically recommended against the use of a bulldozer because of the greater chance of mixing soil horizons and potential damage to evidence because it must drive over the search area (Dupras et al. 2006), in some situations a bulldozer may be an effective tool. Because of the specific method employed in this case, which minimized driving over the top of the search area, we believe this approach can be used when necessary and appropriate, with minimal damage and acceptable results.
The search began by manually excavating specific burial locations identified by a witness. When these attempts were unsuccessful in locating any remains or indications of burials, manual excavations were then conducted at other nearby locations. When these excavations were unsuccessful, archaeologists were requested to provide assistance. Investigators and local anthropologists employed numerous detection techniques, including visual assessment for depressions or alterations, probing, test excavations, ground-penetrating radar, magnetometry, and cadaver dogs. These techniques were also unsuccessful in locating potential grave sites. Soil probing and geophysical techniques were not productive, in part because of the nature of the soil, which was soft and uniform down to approximately four feet.
Investigators felt that all traditional detection methods available had been exhausted, and witnesses could not be more specific about the possible grave location. The amount of search area remaining was immense. Investigators decided to employ heavy equipment in the search with the understanding that if remains were discovered, the machinery would be removed from the search area and traditional manual excavation would follow. Investigators agreed that a backhoe probably would not be able to dig the large area in an appropriate time frame; therefore, one of the authors (GWR) suggested using bulldozers
The decision was also based in part on previous success with locating remains with a bulldozer on a case in Juarez, Chihuahua, Mexico. FBI personnel responded to Juarez in 1999 to assist in the recovery of human remains at five separate search areas, one of which covered five square miles. After conducting visual examinations from the ground and air, personnel used satellite imagery, probing, ground-penetrating radar, cadaver dogs, manual excavation techniques, and, finally, a bulldozer. The machine’s eight-foot bucket scraped approximately four inches of soil at a time from a targeted area and unearthed human bone at a depth of approximately five feet. Once bone was discovered, the machine was removed from the site and traditional excavation methods were used. A forensic anthropologist examined the Juarez remains and reported no postmortem injuries attributable to the heavy equipment.
The Forensic Bulldozer Approach
Bulldozers and operators for this search were provided by the U.S. Forest Service: one machine was a John Deere 450 H (John Deere, Moline, Illinois), and the other was a Caterpillar D-7 (Caterpillar, Peoria, Illinois). Because this was a wooded area and numerous small trees would have impeded the path of the bulldozers, the first “pass” of the machinery was to maneuver over the entire search area, removing only the top few inches of soil (largely containing leaf debris and garbage) and removing the smaller trees. Following this initial pass, the search team walked the area in case any search areas of interest appeared. None were observed.
Rather than having the operator continue to drive over the entire search area, removing a small amount of soil from the top with each pass (which could potentially damage and compact evidence by driving over it), a trench-and-shift technique was utilized. The technique involved digging an initial approximately 4-foot-deep trench at one side of the search area, and then moving laterally approximately 6 inches on each subsequent pass, widening the trench to the side. While excavating the initial trench, the bulldozer passed back and forth over an approximately 100-foot-long strip, deepening the trench by approximately 6 inches with each pass. The search team followed the bulldozer closely, with some members near the front of the bulldozer and some behind (in case it drove over the grave site and left visual indicators). After digging the initial trench, the bulldozer simply passed back and forth through the trench, removing soil from the side of the trench as it progressed in one direction. The advantage of this technique is that, rather than driving on top of the entire search area, the bulldozer arrives at each new area from the side, while the search team watches for evidence and/or related changes in the soil profile. The technique also has a better chance of encountering and discovering remains (if present) than scraping from a horizontal plane, assuming that the body was placed in a horizontal position within the grave.
Although no skeletal remains were discovered, the equipment and search techniques employed were effective and would likely have revealed the grave, had it been located within the search area. As evidence of this, numerous small anomalies were discovered during the search, including pit features, old campfires, a hibernating box turtle (alive and unhurt), and a projectile point.
Although the use of the “forensic backhoe” as a clandestine grave search tool has received some attention in the forensic anthropological and archaeological literature, reference to the use of the forensic bulldozer has been minimal and often negative. The major drawback to its use is that it usually drives over the top of the search area, thereby potentially damaging evidence. Here we have described the trench-and-shift technique, which uses a bulldozer first to dig a trench to one side of a search area and then to remove soil from the side of the trench, thereby limiting machinery movement on the top of a potential grave. The potential for damage using this technique still exists and could include crushing from the tread, if the location or depth is mis-estimated, and possible scraping from the blade as it approaches from the side (although the latter is also of concern when using a backhoe). It also would be important to have a forensic anthropologist examine the bones to determine whether any damage was preexisting or recent and possibly resulting from the equipment.
In the case of a homicide investigation, locating the victim’s remains is critical to determining the cause and manner of death and to the successful prosecution of a homicide. When there are no remains or associated forensic evidence, it may be difficult to successfully investigate a homicide. Moreover, victim discovery and identification are also important for social, legal, and emotional reasons. It is therefore essential to explore every means possible in the effort to systematically locate and recover remains.
Although no grave or body was detected in the case described here, investigators were confident that the area searched could be excluded as the location of the remains. We feel confident (based in part on the discovery of various anomalies and artifacts) that, if they are present in the search area, remains in similar situations can be identified using this strategy. We conclude that although not ideal for reducing potential loss and damage to the evidence, the forensic bulldozer can be used efficiently and effectively with an appropriate team of forensic experts in the search for clandestine graves in certain contexts.
This is publication number 09-21 of the Laboratory Division of the Federal Bureau of Investigation. Names of commercial manufacturers are provided for identification purposes only, and inclusion does not imply endorsement by the FBI. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the FBI or the U.S. Government.
We thank SA Michael Hochrein, of the FBI’s Pittsburgh Field Office; SSA Rex Stockham, of the FBI Laboratory; and Bruce Budowle, formerly of the FBI Laboratory, for their input and assistance in drafting and reviewing this manuscript, and the reviewers for their comments and suggestions. We also thank the U.S. Forest Service and everyone involved in the search effort.
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