The black-and-white shots are the only known contemporary footage of the notorious S-21 - a former school converted by Pol Pot's ultra-Maoist followers into a prison camp.

The films were shot around January 10, 1979, when the camp was discovered by the invading Vietnamese.

About 16,000 people were sent to the camp, chained and allegedly tortured before being sent to their deaths at the 'killing fields' on the outskirts of Phnom Penh.

In submitting the films to the extraordinary chambers set up to try former Khmer Rouge leaders, prosecutors said the footage corroborated claims that conditions inside S-21 - now Tuol Sleng Genocide Museum - were inhumane.

'The images include scenes ... of various types of cells and restraint devices within the S-21 central compound, and decapitated corpses chained to beds in Building A of the compound, among other things,' they said.

Five defendants are scheduled for prosecution, among them Kaing Guek Eav, alias Duch, who ran S-21 and is expected to be tried first when the tribunal officially gets under way on February 17.

Others facing charges of crimes against humanity are former foreign minister Ieng Sary and his wife Ieng Thirith, who was minister for social affairs in Pol Pot's cabinet.

Khieu Samphan, a former head of state, and 'Brother No2' Nuon Chea are also under arrest.

Other senior leaders, including 'Brother No1' Pol Pot, are dead.

Prosecutors said the footage was submitted as evidence after it was reviewed by senior investigator Craig Etcheson and senior assistant prosecutor Tan Senarong. Two segments were ruled relevant.

The first is more than seven minutes long and details an overview of the prison and chained corpses. The second is four minutes long and shows two infants and two older children in poor health being removed from the jail by Vietnamese soldiers.

The footage will also throw the spotlight on Vietnam's awkward relations with Cambodia, which it invaded in late 1978 and occupied for 10 years. In 1979, Hanoi conducted its own trial of Pol Pot and Ieng Sary, sentencing them to death in absentia for genocide. Although that trial was widely considered a legal farce, the evidence submitted was compelling.

In the Vietnamese trial, Vang Pheap, an S-21 guard, described how prisoners met their ultimate fate. Pits were dug and the prisoners were struck with an iron bar. 'After that, Pol Pot's men cut the victims' throats or ripped their bellies to pluck the liver,' he told the court.

Bun Sath, a political officer, told the court of the steady precision required to carry out the leadership's commands. Evenings were preferred because the streets were deserted. Prisoners were bound in pairs and bashed on the napes of their necks.

Up to 300 were killed in a session. 'We began at 6pm and continued until 9pm or 10pm,' the court heard.

Another witness, Sim Phia, told the court: 'Hidden behind a coconut tree, I saw the soldiers take nine children from 10 to 13 years of age out of trucks. The children's arms were tied.

'The soldiers pulled them up to the bridge over the pool. No matter how much they cried or shouted for help, they were thrown in as prey for the crocodiles.'

However, few took the impartiality of the trial seriously. Defence lawyer Hope Stevens said she was an expert on 'genocide, murder, rape, torture, mutilation, lynching and deprivation of human rights' because she was a black American.

She labelled her own clients 'criminally insane monsters'.

In 1996, Norodom Sihanouk, then king, granted Ieng Sary a pardon against the verdict as part of negotiations that led to an end of civil conflict two years later and paved the way for the current tribunal.