But, even in an era of sophisticated forensic science, definitive evidence can be elusive: in one case, the Serbs burned hundreds of corpses in a leadsmelter.
Ever since their homes were destroyed during the war six years ago, more than 500 Roma (Gypsies) have been living in makeshift camps set up by the UN next to a disused - but contaminated - leadsmelter in Mitrovica, northern Kosovo.