Image caption Survivors of Khmer Rouge brutality were among those attending court

The story of Cambodia in Year Zero is unfolding in a quiet courtroom near the capital, Phnom Penh.

The building lies at the end of a lane near one of the roads that the Khmer Rouge marched triumphantly down in April 1975.

In the early morning a line of elderly and often frail people queued to gain admission. Among them were survivors of the Khmer Rouge, along with former guards and officials of the regime.

It is one of the curious features of this trial that victims and perpetrators not only queue together, but in some cases travel to court in the same group.

Hong Huy, who lost eight members of his family during the Khmer Rouge era, travelled on a bus from Svay Sisophon in the north of the country. Sitting behind him was Chim Phan, a former deputy commune chief, who is accused of publicly killing a couple who fell in love without permission from the regime.

"If you did not do what the leaders said then you would have been killed yourself," Mr Phan says. The survivor Hong Huy said he felt no bitterness against people like Mr Phan. It was the top leaders, the people now on trial, who were really to blame.

In court both men listened to the female co- prosecutor, Chea Leng, solemnly described a litany of horror.

Who were the Khmer Rouge? Maoist regime that ruled Cambodia from 1975-1979

Led by Saloth Sar, better known as Pol Pot

Abolished religion, schools and currency in effort to create agrarian utopia

Up to two million people thought to have died of starvation, overwork or by execution

Defeated in Vietnamese invasion in 1979

Pol Pot fled and remained free until 1997 - he died a year later

She recounted the forced evacuation of the population of Phnom Penh, how the roads were littered with the bodies of those executed or killed by hunger and disease.

She told of a man whose liver was ripped out of his body while he was still alive, and of a mother refused permission to bury her two young children who died on the march.

Citing witnesses, Ms Leng said starving patients at a hospital cut the flesh from human corpses and cooked it in order to survive. The prosecutor said one witness "had the impression the world was coming to an end".

Describing the Khmer Rouge regime as an assault on the humanity of the Cambodian people, she told of a campaign of forced marriage "in which the fundamental human emotion of love was removed". The campaign included Buddhist monks who were forced to abandon their vow of celibacy.

Listening to all of this were the three elderly accused. So-called Brother Number Two Nuon Chea, who was second in command to the Khmer Rouge leader Pol Pot, wearing dark glasses and an impassive expression.

Nearby was Khieu Samphan, the regime's head of state, and Ieng Sary, the foreign minister. He complained of back pain and was taken to another room where he watched proceedings via closed-circuit television.

There was a Cambodian school group attending the court. They are teenagers, children of a country that is unimaginably different to the hell on Earth described by the prosecutor.

But for them, and for all of Cambodia, the trial can at least write into history the facts of what happened and act as a warning for the future.