Saturday will mark the passage of two decades since the mass killing of more than 8,000 Muslim men and boys by Bosnian Serb forces in the town of Srebrenica during the Bosnian War. On July 11, 1995, towards the end of the war, Bosnian Serb soldiers swept into a U.N.-designated “safe haven,” taking military-age men, boys, and some elderly men. Over the days that followed, they executed them and dumped their bodies into pits in the surrounding forests. The executions were well-planned, and the Serb army made considerable effort to disguise its activities. While the killings took place over just a few days, the process of finding the bodies took years, and the task of identifying and burying them properly continues to this day—more than 1,000 are still listed as missing. International tribunals have made a number of genocide convictions connected to the Srebrenica killings, and several trials and appeals are ongoing. On Wednesday, Russia vetoed a U.N. resolution that would have condemned the massacre as a “crime of genocide,” claiming the resolution singled out Serbs unfairly, and “would lead to greater tension in the region.”