|Bou Meng (left) and Chum Mey are among only seven people known to have survived S-21
Bou Meng and Chum Mey have waited 30 years for justice. Of roughly 14,000 inmates who passed through the Khmer Rouge's S-21 torture centre, they are two of only a handful to have survived.
|A former high school, Tuol Sleng's playgrounds
and classrooms became a centre of brutality
S-21 was once a school known as Tuol Sleng. It lies in an anonymous backstreet of the Cambodian capital, Phnom Penh.
Once its yards echoed to the sounds of children playing.
Under the Khmer Rouge it became a centre of torture and execution.
For the two men, revisiting Tuol Sleng - now a museum to the horrors of the Khmer Rouge - is an emotional journey.
Looking at the fading blood splatters on the walls of the crumbling former cells Bou Meng breaks down.
Chum Mey tries to console him. "They beat me for 12 days and 12 nights," he recalls.
"When eventually I was in too much pain I told them, I had joined the CIA, the KGB whatever they wanted.""It wasn't really a confession because I didn't answer truthfully. But they stopped beating me."
He still struggles to understand why he was held here and tortured."I didn't do anything wrong. They killed my wife and my children and they didn’t do anything wrong. Why did they kill my family?"
Bou Meng also lost his wife to the Khmer Rouge.
And he still bears the physical scars of the beatings he received at their hands.
Those wounds have healed, but the emotional damage has not.
|Chum Mey shows how he was shackled
in one of S-21's tiny cells
He believes the only reason he survived because of his skill as a painter.
"One day they came in here and they asked can anyone draw? I raised my hand and said I could paint.
"They asked me to draw a picture of Brother Number One, Pol Pot.
"They said your pictures must be 100 per cent accurate. If they aren't, we'll kill you and you’ll be fertiliser on the rice fields."
For visitors to Cambodia today, S-21 is museum - a place for the curious to wonder and abhor.
For Bou Meng and Chum Mey it remains a prison – one they will only be able to escape once the people who put them there are themselves jailed.
"I'm still angry the leaders are free," says Chum Mey.
"Khieu Samphan was head of state of Democractic Kampuchea and Nuon Chea. Why do they say they don't know about the killing? It's unbelievable."
Both men are now old and frail and had long feared they would not live to see any trials or attempts to find justice in Cambodia.
|Tuol Sleng is a grim memorial to
Cambodia's brutal past
Now that the process is underway, they feel new reasons to be afraid.
"You see we are S21 survivors," says Chum Mey. "We will be eyewitnesses for the trial, and it may be that someone wants to kill us so there are no more eyewitnesses.
"If you have no eyewitnesses how can you have trial?"
Nonetheless they both say they are determined to testify."If my generation can kill each other we should do something to avoid it happening again," says Chum Mey.
For Bou Meng, Chum Mey and millions of other Cambodians, this trial process is a chance to write the final chapter of the long national nightmare.