The Khmer Rouge tribunal on Thursday handed down life sentences to two of the regime's most senior leaders, calling the crimes the cause of "immeasurable harm."

Brother Number Two, Nuon Chea, 88, and Khmer Rouge head of state Khieu Samphan, 83, were found guilty on charges of crimes against humanity for their role in the forced evacuation of millions and a mass execution of enemy soldiers.

Reading the verdict out, chief judge Nil Nonn called the sentences reflective of the grave nature of the crimes.

"There was a widespread and systematic attack against the civilian population of Cambodia… this attack victimized millions of civilians throughout Cambodia."

Over the course of an hour-and-a-half, Judge Nonn detailed the litany of crimes against humanity covered in the case, including murder, extermination, political persecution, and inhuman acts.

In a second case set to begin in September or October, the pair will face charges related to genocide, rape, forced marriage, purges and a slew of other crimes.

'Killing Fields'

An estimated 1.7 million Cambodians died of starvation, exhaustion and execution, during the regime's three years, eight months and 20 days in power.

After taking over Phnom Penh in April 1975, the Khmer Rouge sought to install a Maoist-inspired agrarian society by forcing millions into forced labor. To create its collectives and dissolve any sense of ownership or family ties, the regime moved virtually the entire population from their homes to elsewhere.

The most extreme evacuation was that of Phnom Penh beginning on April 17, 1975. Forced from homes, schools and even hospitals, at least 2 million residents representing the city's entire population were told it was necessary to leave because of impending American bombings - a false pretense - and were assured they would spend only a short time away.

A harrowing ordeal, recounted at times during the trial in wrenching testimony, the evacuation exacted a fatal toll. Without access to food water or medical care, thousands died en route.

At court Thursday morning, Judge Nonn recounted the testimony of several civil parties who testified during the two-year trial, delving into tragic detail of the forced evacuation.

One, "recalled seeing a Khmer Rouge soldier tear apart a crying baby who was crawling on his dead mother's body," he told the court.

As Judge Nonn read out the summary judgment, both defendants appeared impassive. The courtroom appearance of Nuon Chea - in a wheelchair and unable to stand - marked the first since closing statements in October of last year. Frail and frequently ill, he spent much of the later days of the trial in his holding cell.

Neither man made a statement, the only words coming when Nuon Chea barked at a judge that he was unable to stand during sentencing.

Following sentencing, lawyers from both defense teams said they would be appealing.

"The reaction of our client was basically that he expected this judgment, that he was not surprised at all that this judgment was issued," said Victor Koppe, a lawyer for Nuon Chea. "He didn't have any faith or confidence in this [court] and he got confirmed in that suspicion."

High emotions, long case

Hundreds of civil parties, students and dignitaries were in attendance for the announcement, some breaking down into tears after the verdict was delivered.

"I didn't feel very calm, I wasn't happy to hear that verdict because life in prison is not enough. They killed so many people. What I want is an execution right now," said Pech Srey Pan, 65, a civil party who was evacuated from Phnom Penh when the Khmer Rouge took over the city.

For many, however, a life sentence was precisely what they had hoped for.

"I'm very happy to see the verdict," said Heng Buneth, a 45-year-old who saw his father – a Lon Nol soldier – executed and who was orphaned during the Khmer Rouge.

Chea Leang, the national co-prosecutor, welcomed the sentence saying in a press conference held after the case that the sentences were "the only appropriate sentences the chamber should have handed down."

"The judgment wont turn back time, it wont give back life to those executed, or those who died of heat or exhaustion, of lack of food or water or medical assistance, it wont rebuild families broken in every part of Cambodia because of lost sons, daughter, wives, and husbands," she continued.

"However I think it will give some justice, reinstate some respect to those victims that have been denied to them for so long."

Slow moving trial

But while many are pleased with the outcome, it comes following a particularly rocky trial. The case against the regime's top living leaders was intended to be the cornerstone of the Khmer Rouge tribunal, instead it had been marred by allegations of corruption, mismanagement and political interference.

The slow movement of the UN-backed tribunal, meanwhile, wrecked havoc on a case involving numerous aged defendants, victims and witnesses.

Between November 2011, when opening statements began, and the close in October 2013, half of the defendants fell out. Foreign Minister Ieng Sary died in March 2013, while his wife, Social Affairs Minister Ieng Thirith was in September 2012 declared unfit to stand trial due to dementia.

Cambodian Deputy Prime Minister Sok An admitted there had been "hiccups" but said the sentence was historic.

"We never lost sight to seek justice for the victims of the Khmer Rouge, today, we welcome the delivery of justice."

The sentencing of the pair marks only the second conviction for the eight-year-old court.

In February 2012, Kaing Guek Eav, alias Duch, was sentenced to life in prison, on appeal, for overseeing the notorious S-21 security center. An estimated 12,000 people were executed at the jail, following a torturous interrogation process.

Two more cases against four mid-ranking cadres are currently under investigation, but the government has been adamant that it wants no trials beyond the current case and court officials have repeatedly attempted to shut down investigations.

“This trial will hopefully pave the way for a much more efficient second trial,” said Heather Ryan, a trial monitor for Open Society Justice Initiative.

“[If only this case is heard] that's a limited picture of crimes committed during the Khmer Rouge period, which is the reason why the second trial in Case 002 is important, why trial 003 and 004 are important to give a broader picture of the nature and magnitude of the crimes committed.”

Additional reporting by Neou Vannarin