Hidden graves give up their secrets to geologists

Scientists buried pig carcasses in eight different soil and meteorological areas in Colombia, including this site near Marengo, where the team is tracking how weather affects the soil and body decomposition.


Carlos Molina

As of April 2013, more than 61,000 people were registered as missing in Colombia, many of whom are feared to be victims of the country’s narcotics-fueled gang wars and, presumably, buried in clandestine graves. Now a new study comparing the most effective remote sensing tools for finding hidden graves may help bring justice for victims and closure for families.

Until recently, the main tools available for searching out hidden graves in Colombia were a metal pole — used to probe for areas of unconsolidated soil that might contain remains — along with a metal detector and dogs trained to sniff out human remains.

“The lack of geophysical tools has cost excess time and money and returned a limited success rate,” says Carlos Molina, a forensic geologist at the National University of Colombia in Bogotá and lead author of the new study, presented at the American Geophysical Union’s Meeting of the Americas in Cancún, Mexico, in May.

To encourage the use of geophysical tools — such as ground penetrating radar, electrical resistivity, bulk ground conductivity and gradient magnetometry — for finding hidden graves, Molina and colleagues began conducting a series of experiments to determine which remote sensing methods work best in Colombia’s variable soil types.

The team has buried pigs — often used to simulate human bodies in forensic tests — in eight different grave locations that represent the varying soil types and climates around Colombia.

“Soil type is a major factor,” says Jamie Pringle, a geoscientist at Keele University in England and a collaborator on the project. “In sandy-type soils the radar works pretty well, but in more clay-rich soils, electrical resistivity is usually the better tool.”

The graves were resurveyed every eight days during the first month and every 15 days in the second and third months. The sites will continue to be checked monthly until December, 18 months after the burials. “It does get a bit grisly,” Pringle says, “but there’s really no substitute for studying a real decomposing body.”

Resurveying the graves over 18 months will help investigators develop a set of guidelines to determine more accurate timelines for crime scenes, Pringle says. “One of our main goals is to study how graves and bodies change over time. There have been a handful of these simulated burial studies, but few have extended over the time period we intend to study.”

“This is a very comprehensive and ambitious project,” says Ray Murray, a forensic geologist and professor emeritus at the University of Montana in Missoula who was not involved in the new project. “Establishing a timeline for a burial is very difficult, in part because it hinges so much on climate and the type of soil.” Thus, Murray says, “localized studies are often very important.”

Other long-term studies looking at the decomposition of bodies over time have been conducted elsewhere, most famously at the University of Tennessee’s Forensic Anthropology Center in Knoxville, which inspired the crime novel “The Body Farm” by Patricia Cornwell. But few studies have focused specifically on testing remote sensing methods for finding relatively recent graves, Murray says.

“Hopefully, this project will provide a significant advance [in efforts to use] quick and effective geophysical tools and create a methodology to speed up the search procedure to help find missing people, bring perpetrators to justice and provide closure for families,” Molina says.

Mary Caperton Morton
Thursday, August 8, 2013 - 09:00