THE MOST CHILLING EVIDENCE OF HUMANS' PROPENSITY FOR ATROCITY IS that the investigation of war crimes has become an exact science. Starting with the 9,000 Argentines who were "disappeared" in that country's dirty war of 1976 to 1983, forensic pathologists and anthropologists have honed their techniques in El Salvador, Guatemala, Haiti, Rwanda and now in the formerYugoslavia. Finding a pile of bodies isn't enough: investigators need evidence that victims died not in battle but at the hand of an executioner. War-crime detectives, though, have a deeper motivation for their work. "We are creating an historical record that will withstand revisionism and fading memories," says Dr. Robert Kirschner, who heads the forensic program at Physicians for Human Rights, a group investigating Balkan war crimes.
Using tools no fancier than shovels, tape measures and brushes, the investigators piece together a narrative of death. First a team probes a suspected grave site with a long pole, feeling for changes in density that suggest soil has been dug UP and then replaced, and sniffing for the characteristic odor of decomposition. Then the team surveys and maps the grave's surface features, looking for evidence--like spent cartridges--that executions took place there. At a mass grave near Vukovar, Croatia, a PHR team found more than 75 spent cartridges in the burr bushes northwest of the grave; none was found to the northeast or south. Numerous bullet marks scarred the acacia trees southeast of the grave, but nowhere else. Clearly, this was not the site of a battle, where bullets fly in all directions.
Next, the investigators dig a test trench and locate the bodies. "Their position can tell you whether the victims were lined up and shot, or whether they were bulldozed into the grave after being killed," says Kirschner. At the Vukovar site, PHR deduced that the executioners "fined up along the northern boundary of the grave ... and fired at their captives to the south and southeast."
But whose bodies are buried there? "We can determine a murder victim's age, sex and race from the size and shape of certain bones," explains forensic anthropologist Clyde Snow, who is investigating mass graves in Croatia. Sex is writ in the pelvic bones (in men, the iliac bone is more highly arched, a bone near the hip more sharply notched) and skull (men have larger brow ridges, bigger jaws and longer bones behind the ears). The dead also tell their age. The ends of the long limb bones close in the late teens, and the ends of the ribs become progressively more calcified; sutures in the skull do not fully fuse until the age of 50. A skeleton can even reveal handedness. In a rightie, the right forearm is typically a few millimeters longer than the left, and muscle attachments are larger.
Most important, bones can describe the circumstances of death. "If in a mass grave everyone is shot at the base of the skull, that's not typical of combat," says Kirschner. "And if the dead all show the same kinds of wounds, in the same place, you can guess that the victims were lined up and shot. Combat wounds are variable in location and size." And fatal injuries from machetes look different from damage to a corpse. "If a [bone] fractures before death, it is neat and linear," he explains. Investigators can determine whether a victim was beheaded, as in Rwanda, or if the head of a corpse was severed accidentally by, say, a bulldozer. Still, science can accomplish only so much. "In more than a decade of identifying [war crimes] victims," Snow recently wrote, "my findings have led to convictions and jail sentences only once."