PHNOM PENH, Cambodia – Three and a half decades after the genocidal rule of Cambodia’s Khmer Rouge ended, a U.N.-backed war crimes tribunal today sentenced two top leaders of the former regime to life in prison on war crimes charges for their roles during the country’s 1970s terror.

The historic verdicts were announced against Khieu Samphan, the regime’s 83-year-old former head of state, and Nuon Chea, its 88-year-old chief ideologue – the only two surviving leaders of the regime left to stand trial.

The tribunal’s chief judge Nil Nonn said they were guilty of “extermination encompassing murder, political persecution and other inhumane acts comprising forced transfer, enforced disappearances and attacks against human dignity.”

Nearly a quarter of the population – about 1.7 million people – died under rule of the Khmer Rouge from 1975-79.