07/08/2014 05:23 BST | Updated 07/08/2014 05:59 BST

Khmer Rouge Last Surviving Leaders Convicted Of Crimes Against Humanity

Three and a half decades after the fall of Cambodia's Khmer Rouge, two top leaders of the former regime have been sentenced to life in prison for crimes against humanity during the country's 1970s reign of terror that left millions dead.

Nuon Chea, 88, served as leader Pol Pot's deputy and Khieu Samphan, 83, was the Maoist regime's head of state.

They are the first top-level leaders to be held accountable for the regimes brutal crimes.

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Khieu Samphan, former Khmer Rouge head of state

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Nuon Chea, who was the Khmer Rouge's chief ideologist and No. 2 leader

Up to two million people - nearly a quarter of the population — are thought to have died under the 1975-79 Khmer Rouge regime - of starvation and overwork or executed as enemies of the state.

Judge Nil Nonn said the men were guilty of "extermination encompassing murder, political persecution, and other inhumane acts comprising forced transfer, enforced disappearances and attacks against human dignity".

Survivors of the regime traveled from across the country to witness the historic day, the Associated Press reported.

The several hundred seats available to the public at the tribunal were packed as the verdict was read. Many who attended said they felt mixed reactions to the verdict and questioned if any punishment could fit the crimes committed by the Khmer Rouge.

Photo gallery Khmer Rouge See Gallery

Many have criticised the slow justice, however, and its cost.

"The crimes are huge, and just sentencing them to life in jail is not fair," said 54-year-old Chea Sophon, who spent years in hard labor camps building dams and working in rice fields. His brother was killed during the Khmer Rouge era.

"But what can I do? I just accept the verdict," he said, but then added: "Even if they die many times over, it would not be enough."

Outside the court, Khmer Rouge survivor Nou Saota told the BBC: "I feel so happy and relieved. A huge burden has been lifted off me."

Youk Chang, another survivor, told the BBC the verdict was "a little too late for many" but said it was vital the trial took place.

"It's important for the young population to learn this lesson so that we can prevent such atrocity from occurring anywhere, not just in Cambodia," he said.

The two men had insisted they were not guilty and their lawyers said they would appeal against the judgement. “It is unjust for my client. He did not know or commit many of these crimes,” Son Arun, a lawyer for Nuon Chea, told journalists, according to the BBC.

They will remain in detention while this takes place.

The Associated Press reported that the two men now face a second trial due to start later this year where they will face charges of genocide. That trial is expected to take years to complete.

Legal campaigners welcomed the decision. James Goldston of the Open Society Justice Initiative, which has monitored the tribunal since it was first established, said “Nearly forty years after some of the 20th century’s most appalling crimes were committed, the victims have seen the perpetrators brought to account before a court of law. They have been tried fairly, and found guilty.”

Rights group Amnesty International, meanwhile, called the ruling "an important step towards justice", as it noted "troubling" obstacles the court had faced.