The Butterfly Hunter

Margaret Cox searches for butterflies, but there's no joy if she finds them. They are the by-product of what she terms a "geophysical anomaly". We know it by its common name: a mass grave.

In the butterfly kingdom, each species feeds on a specific "host" plant. There is a blue butterfly that feeds only on Artemisia vulgaris or mugwort, a wild flower that grows to 4ft, about the height of a child. The people of medieval Europe stuffed pillows with mugwort believing it would give them happy, vivid dreams. They thought it magical, a charm.

Some years ago in the Balkans, clouds of blue butterflies gathered on dense banks of Artemisia that had flourished all of a sudden. A change in the soil's nutrient levels and a disturbance of dormant seed banks had led to this dense colonisation. It was 1999, and the plants were blossoming in Kosovo.

In the 1990s, mass graves hid the victims of Kosovo's genocide in which Albanian Kosovans where killed by Serbs. But the dead are not that easy to hide. They leach into the soil, raise the nutrient level, feed the weeds, lure the butterflies. No vivid, happy dreams. Not for anyone.

Not least for Cox. On first meeting at her cramped Bournemouth office, it is easy to imagine Cox as the archetypal lepidopterist, collecting rare species for her display cabinets. A slight woman of average height with a rolling Dorset accent and healthy country glow, it is certainly hard to picture her waist-deep in the decaying remains of thousands of dead people.

But Cox swapped her wellingtons for the steel-capped boots and Tyvek suit of the forensic anthropologist a long time ago. The gentle Dorset accent remains but it does little to soften the impact of the atrocities her work involves.

It is Cox's job to locate, excavate and exhume mass graves believed to hold the victims of genocide. Her brief is twofold: to retrieve the evidence for the courts and international tribunals, enabling them to convict those responsible and, secondly, to identify and return the exhumed remains to their families. This is what she describes as "the desired end point. That remains go back and are buried by people to whom they mean something and who can then move on with their lives."

This weekend marks the 10th anniversary of the end of the Rwandan genocide: one of the atrocities Cox has investigated. For most, the mass graves of genocide symbolise the worst aspects of humanity but for Cox they are the beginning of justice: "both a symbol of despair and of hope". It is a view shared by her colleague, forensic anthropologist Dr Mark Skinner, who says: "Unexcavated, they can function as political tools to intimidate survivors; scientifically excavated they are threats to the perpetrators."

And it is this search for a just resolution to unjust events that enables Cox to continue with such seemingly hopeless work. But before the harrowing processes of excavation and exhumation can begin, and the wheels of justice finally turn, the graves must first be found.

It is hard to imagine that the bodies of thousands of men, women and children could be hard to find, but they are. Any murderer trying to avoid prosecution hides the evidence - the body - so too with the perpetrators of genocide.

Cox has spent much of the past 10 years working for Inforce (International Forensic Centre of Excellence), an organisation she founded. She has been to Eastern Europe, Iraq and Africa with Inforce, hunting down the past with the science of the future.

Thermal-imaging can pick up temperature differences in the ground. A decaying body heats up, so mass graves packed with hundreds of bodies give a very clear thermal image. "Geophysical prospection" or "remote sensing" can detect whether there has been any ground disturbance. Soil-resistance surveys, ground- penetrating radar, magnetrometry and cadaver dogs are all used to find the buried. And aerial and satellite imagery help detect grave sites.

But as the techniques and technology of those hunting the killers increases, so too do the mechanics of concealment.

"There was one grave that was considered to be very important for indictment purposes, says Cox talking about her work in Kosovo. "It was related to the massacre of women and ` children in a specific place and we were asked to find that grave. By that stage the perpetrators knew that satellite imagery was being used, so they changed their modus operandi. Instead of digging mass graves, they moved towards burying people in individual graves in legitimate cemeteries in Kosovo. The area that we had to look at had spoil from building sites put all over it - you can't use geophysics on uneven ground. Also, it had been littered with metal waste and you can't use any test that is based on any sort of magnetic-field anomaly where you have got metal. So, with circumstances like that, the first thing you have to do is remove the spoil - and hope that it is not booby- trapped."

Booby-trapping of graves is a real risk for Cox and her team. She says that in the former Yugoslavia "there was deliberate mining of graves to deter investigators. Razor-blades were put inside body cavities to either harm or deter the pathologists from doing their work. The genocide is highly systemised and disposal and deterrent is all built into the process."