Four now old and infirm members of the the Khmer Rouge's ruling elite are facing a war crimes tribunal, decades after their plans for a Communist Party utopia in Cambodia killed around 1.7 million people by execution, medical neglect, overwork and starvation.
The UN-backed tribunal, comprising Cambodian and foreign jurists, will begin trying them on charges including crimes against humanity, war crimes, genocide, religious persecution, homicide and torture.
With Khmer Rouge leader Pol Pot long dead, this may be the nation's best chance to hold architects of the "Killing Fields" and the enslavement of millions of Cambodians accountable. All four say they are innocent.
Nuon Chea, 84, was Pol Pot's deputy and the group's chief ideologist. Khieu Samphan, 79, was its former head of state. Ieng Sary, 85, was its foreign minister, and his 79-year-old wife, Ieng Thirith, was minister for social affairs.
Together, they form what the tribunal calls Case 002. The chief jailer of a notorious Khmer Rouge prison was convicted last year in the breakthrough Case 001. Political and financial pressures on the tribunal are raising doubts over whether there will ever be a Case 003.
Although this week's court sessions will be strictly procedural, with testimony and presentation of evidence expected to begin in August or September, it will mark the first joint appearance of the defendants in the dock, 32 years after the Khmer Rouge was kicked out of power in 1979 with the help of a Vietnamese invasion.
Pol Pot escaped justice with his death in 1998, then a prisoner of his own comrades as his once-mighty movement, in jungle retreat, was collapsing.
The tribunal, officially known as the Extraordinary Chambers in the Courts of Cambodia, started operations in 2006. Its first defendant was Kaing Guek Eav, also known as Duch, commandant of Tuol Sleng prison, known as S-21, where only a handful of prisoners survived.
Up to 16,000 people were tortured under Duch's command and later taken away to be killed.
Duch, now 68, was sentenced to 35 years in prison for war crimes and crimes against humanity. His sentence was reduced to a 19-year term because of time previously served and other technicalities, bringing angry criticism from victims who called the punishment too lenient. Cambodia has no death penalty.