PHNOM PENH, Cambodia — They were leaders of Cambodia’s infamous Khmer Rouge, the fanatical communist movement behind a 1970s reign of terror that transformed this entire Southeast Asian nation into a ruthless slave state – a place where cities were emptied of their inhabitants, religion and schools were banned, and anyone deemed a threat was executed.

When the nightmare ended, in 1979, close to 2 million people were dead – a quarter of Cambodia’s population at the time.

On Thursday, a U.N.-backed tribunal convicted two of the once all-powerful men who ruled during that era of crimes against humanity in the first and possibly the last verdicts to be issued against the group’s top members.

Although survivors welcomed the decision to impose life sentences against Khieu Samphan, an 83-year-old former head of state, and Nuon Chea, the movement’s 88-year-old chief ideologue, they also say justice has come far too late.