Pioneering technique to help identify mass graves
By using electric current through the subsurface it is possible to locate buried bodies and objects. Its application in the forensic field would support searching for missing people, victims of forced disappearance in Colombia.Bogotá D. C., 23 de marzo de 2016 — Agencia de Noticias UN-
Up to June 30 of 2015, there were 75,000 reported cases of missing people in Colombia of which 21,000 were forced disappearances.
They dug 12 pits, 8 of which were at the UNal Centro Agropecuario Marengo and 4 at the Universidad de los Llanos.
This is about a forensic laboratory which mimics the conditions of mass graves in Colombia. For this Carlos Martín Molina Gallego a Universidad Nacional de Colombia (UNal) forensic geologist (unique in Colombia) and member of the UNal Geophysics Research Group used geophysics to support his research project and locate missing bodies and objects underground.
According to Molina, currently authorities use a stainless steel rod in places where informants have indicated the presence of mass graves, an obsolete technique, to say the least.
Pigs and skeletons
To confirm the efficiency of the method they dug 12 graves 8 at the UNal Centro Agropecuario Marengo in the municipality of Mosquera (Province of Cundinamarca) and 4 at the Universidad de los Llanos, in Villavicencio (Province of Meta) with the purpose of confronting geophysical responses.
Taking into account that the anatomy, physiology and genetics of pigs is similar to humans, as well as the decomposition process; they buried 3 - 70 kilo specimens in 2 graves and 3 human skeletons face up with 9 mm gun impacts in 2 other graves. They also placed 3 human bones remains to mimic beheading and incineration scenarios and left 3 graves empty as control.
The project included monthly monitoring activities during 2 years using a Ground Penetrating Radar (GPR) to detect objects and structures under the ground surface.
To detect materials such as bones, rock and minerals they calculated the magnetic sensitiveness, conductivity or resistance of the object to electrical currents.
“We surveyed the area with the team to create a magnetic field which would allow us to identify where the remains were buried,” said Molina.
They also considered other variables such as temperatures, texture and rainfall, in other words the percentages of sand, clay and soil moisture. According to the type of soil and its properties, each team worked differently, for instance the GPR does not detect buried objects when the soil is too clayey and moist, and it is most efficient in dry terrain.
Moisture has a bearing on resistivity and conductivity because the moister the land, it is easier to discover objects capable of transmitting electricity or heat.
“There are many factors which need to be considered, therefore before searching the graves it is necessary to develop a desktop stage to observe satellite imagery, aerial photographs and soil maps. Based on this information they determine which equipment is the most suitable and pertinent,” he said.
One of the main conclusions of the project was identifying graves thanks to efficient geophysical methods. In fact, in the Bogotá savannah the team in charge of measuring resistivity identified all the graves even though they were empty. On the other hand, conductivity did not work in this area due to lack of soil moisture.
In the eastern plains, the method applied discovered all the graves which had pigs and skeletons. Furthermore the GPR achieved 96% effectiveness recording most of the anomalies of the land, except empty graves.
Molina says this is the first time these types of geophysics equipment are used to search for dead bodies; therefore they are suitable tools to quicken search processes and area analyses, where there is a suspicion of mass graves. Furthermore the method designed may be applied also in countries of the intertropical strip as the chemical and physical properties of the soil are similar.(Por: Fin/AVC/DMH/APBL