In the heart of Cambodia's capital Phnom Penh, a former secondary school has been transformed into a monument of horrors. The torture museum Tuol Sleng, translated as "the Hill of the Poisonous Trees", provides a record of the genocide committed during the 1970s by the Khmer Rouge, a communist party that ruled the country for five years.
In one room, rusted torture implements and bloodstains on the ceiling testify to the suffering; in a long hall, photographs of the 17,000 people murdered there, including children, stare back at visitors.
The four men who went on trial this week in Phnom Penh are the highest ranking members of the Khmer Rouge who are still alive. They are, allegedly, the engineers of Tuol Sleng and the murderous campaign against their own people that killed about 1.7 million, more than one quarter of the population.
All four - Ieng Sary, Nuon Chea, Khieu Samphan and Ieng Thirith - are old men in their late 70s or 80s. More than 30 years after the fall of the Khmer Rouge, there have been questions about the merits of trying elderly, infirm men who might not live to see the end of the proceedings, much less serve a full sentence. The leader of the Khmer Rouge, Pol Pot, died a free man in 1998.
The war crimes tribunal is long overdue - but that is all the more reason to demand justice. The leaders of the Khmer Rouge committed some of the worst crimes against humanity of modern times. Tuol Sleng shares the same notoriety as Kibuye stadium in Rwanda, Srebrenica in Bosnia and Auschwitz in Poland.
The trial of these four men is not only about holding them accountable for their crimes. The Khmer Rouge's social engineering folly affected the entire population - essentially every Cambodian who is now over the age of 40 was either a victim of the regime or complicit in its crimes. But there is no question of trying to track down every suspect in a country that is so eager to move on and develop its economic potential.
This trial is a collective opportunity to expose the wounds of the past so that they can begin to heal. Dozens of witnesses have come forward to recount the ordeals that for too long have been remembered in silence.
"This is, at this time, the most important trial in the world," Stephen Rapp, the US envoy on war crimes issues, told the Associated Press. "It's a message to others who might commit similar crimes that there will be consequences."