Image caption Decades after the Khmer Rouge fell, its leaders are going on trial

Thirty-three years. That is how long it has taken to bring the leaders of the Khmer Rouge to account for the atrocities committed when they governed Cambodia in the late 1970s.

The ultra-Maoist organisation led by Pol Pot evacuated towns and cities, forced their former inhabitants into slave labour in the rice fields, and summarily executed anyone considered an "enemy of the revolution".

But so much time has passed that the majority of Cambodians have no memory of the horrors of the Khmer Rouge era.

Now, at last, the three most senior surviving leaders of the organisation are going on trial.

They are Nuon Chea, also known as Brother Number Two, the right-hand man of the late Khmer Rouge leader Pol Pot; Khieu Samphan, who served as head of state during the Khmer Rouge era; and Ieng Sary, the foreign minister and international face of the organisation.

The charges they face include genocide and crimes against humanity. But their day in court has come too late for many of those who lived through the nightmare the three men are accused of causing.

Trials split

The death of Vann Nath in September highlighted the issue. He was one of just a handful of survivors from a notorious Khmer Rouge detention centre - and a well-known campaigner for justice.

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

But he did not live long enough to see those who set up the nationwide network of brutal prisons explain their actions.

Time has taken its toll on the alleged perpetrators as well. Pol Pot died in 1998; his military commander Ta Mok was in custody at the time of his death in 2006. Ieng Thirith, the former social affairs minister and wife of Ieng Sary, has escaped prosecution after developing Alzheimer's disease.

All of this makes the work of the UN-backed Khmer Rouge tribunal seem agonisingly slow. The judges were sworn in more than five years ago - and the defendants have been in custody since 2007. But only now are they going on trial.

A belated sense of urgency appears to have crept in. The judges have decided to split the case against the three surviving leaders into a series of "mini-trials", in the hope of reaching verdicts more quickly.

"The judges have severed the cases into segments so we get to a result," says the international co-prosecutor, Andrew Cayley. "Their major concern was that the accused would pass away before we got to a conclusion. That's why we're dealing with forced displacement first before moving on to other crimes.

"The tension here is that the Cambodian people will want much more dealt with than just the forced displacement. There will need to be further mini-trials for this court to leave the right kind of legacy."

'Want to know why'

Whatever happens in the trials, many Cambodians have already decided on the guilt of the accused. The evidence has been piling up for years - much of it in the research facility known as the Documentation Center of Cambodia, or DC-Cam.

I'm continuing to pursue justice and engage victims - just not through this sham court Theary Seng, Civil party to the trial

Its director, Youk Chhang, has travelled the country interviewing former Khmer Rouge members and the people they tormented. Much of his research has ended up in the hands of the prosecutors at the tribunal.

But he says that what survivors of the Khmer Rouge era really want to hear is an explanation from the organisation's leadership.

"People want to hear why the Khmer Rouge killed their own population, why Cambodian killed Cambodian. This question has been asked for 30 years. On the village level, all the killers were your neighbours, your friends - but Cambodians find that difficult to accept," he said.

"People just want to confirm that the Khmer Rouge leadership were guilty of crimes against their own population - and that's going to be very important for the whole country to move beyond victimhood and develop."

The Khmer Rouge tribunal originally set out to allow survivors to play a direct role in the judicial process.

Its "civil party" system gave victims a voice in court on a similar footing to the prosecution and defence, and was held up as a pioneering example of what international criminal justice could mean to the people who had suffered.

But over time, the civil parties' role has been whittled away - much to the disappointment of those who signed up to take part. Adding to their disillusionment has been a never-ending series of controversies at the court - including allegations of political interference, judicial incompetence and corruption.

'Poor man's therapy'

All this has led Theary Seng to give up on the tribunal altogether. She lost both her parents in the Pol Pot era and was the first person to sign up as a civil party.

Image caption Theary Seng, who lost her parents, has lost faith in the tribunal process

Now she has withdrawn from the process - and she is putting her energy into producing dartboards printed with the faces of the Khmer Rouge leaders.

"This is the poor man's therapy - a way of releasing aggression from the humiliation and suffering of the past," she said.

"But we also offer humour-coated education. With each dartboard pack, we provide educational materials from the Khmer Rouge tribunal, some of which are well-researched documents from the court. I'm continuing to pursue justice and engage victims - just not through this sham court."

While Ms Seng will be absent, hundreds of people are still likely to attend each day of the trial. Many more will follow the proceedings on live television.

Like Youk Chhang, a lot of them will be hoping that the tribunal can produce a definitive version of Khmer Rouge history - which can be handed down not just to Cambodia's current youthful population, but to future generations.

At the very least, this is a chance for survivors to see for themselves that the former Khmer Rouge leaders are, at last, in the dock. Perhaps they will even receive the answers they have been waiting for all this time.