The last two surviving leaders of Cambodia's brutal Khmer Rouge regime of the 1970s were found guilty Friday by an international tribunal on charges of genocide, crimes against humanity and war crimes.

The conviction of Nuon Chea, 92, the chief lieutenant of the regime's infamous leader, Pol Pot, and Khieu Samphan, 87, the former head of state, is the first official acknowledgement that at least some of the estimated 2 million people who died at the hands of the Khmer Rouge from 1975 to 1979 were victims of an orchestrated genocide.

Samphan was in court and appeared stone-faced as the verdict was read by Judge Nil Nonn of the United Nations-backed Extraordinary Chambers in the Courts of Cambodia. He and Chea — who suffers heart problems and watched the proceedings from a separate room — were sentenced to life in prison, the same sentence they are already serving after earlier convictions for crimes against humanity.

Specifically, Friday's verdict establishes that the Khmer Rouge committed genocide against the country's Vietnamese and Cham minorities.

As The Associated Press notes:

"The Khmer Rouge sought to achieve an agrarian utopia by emptying the cities to establish vast rural communes. Instead, their radical policies led to what has been termed 'auto-genocide' through starvation, overwork and execution.

"The crimes against humanity convictions covered activities at work camps and cooperatives established by the Khmer Rouge. These offenses comprised murder, extermination, deportation, enslavement, imprisonment, torture, persecution on political, religious and racial grounds, attacks on human dignity, enforced disappearances, forced transfers, forced marriages and rape."

The Khmer Rouge came to power in the instability that swept through Southeast Asia in the wake of the Vietnam War. The regime was ultimately toppled by a 1979 Vietnamese invasion.

Although Chea and Samphan have suggested in the past that they are victims of a political vendetta, in 2013, they acknowledged a degree of responsibility for the atrocities committed in their names.

Michael Sullivan, reporting for NPR from neighboring Thailand, says that the U.N. backed tribunal has spent 10 years and more than $300 million seeking justice for those who died.

"Only five people have been put on trial, with three convicted. The other two died during the proceedings. Cambodia's prime minister Hun Sen — himself a former Khmer Rouge cadre — has made it clear he wants today's convictions to be the last, though others disagree," Sullivan says.

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