Three decades have passed since Vann Nath was freed from the horrors of the Cambodian torture centre S-21.

He spent those 30 years waiting patiently to see the perpetrators of the crimes inflicted upon him, and thousands of others, brought to justice.

Nath was arrested by the Khmer Rouge and was eventually brought to the capital, Phnom Penh, and taken to S-21 - the high school turned torture centre better known today as the Tuol Sleng genocide museum.

He was trained as a painter in the northwestern city of Battambang, and his ability to paint saved him from almost certain death. 

The artist  was given a photograph of Pol Pot and was told to paint Brother Number One’s portrait and that portrait only.

After the fall of the regime he turned to painting full time, using art to continue to show the world what life was like under the Khmer Rouge.

"People come to ask me about my life and the lives of Cambodian people at that time," he told Al Jazeera, when he was interviewed in 2009.

"I find it very difficult to explain what my life was like in S-21. There is only one way - I am a painter, so I paint to show people what it was like."

But his concern even then was that he would not live to see justice served.

"I have been waiting for the trial, for justice for a long, long time," he said.  "All my friends who survived S-21, there were seven who survived, four are dead."

With Nath’s death there are now only two - Bou Meng and Chum Mey.

His death comes as the tribunal itself is under increasing scrutiny for the slow pace of justice.

Since its inception in 2006, $100m has been spent on the tribunal , yet only one person Kaing Guek Eav - the former director of S-21 - has been convicted. And even his 19-year sentence is under appeal.

Case Two, in which the four most senior leaders Noun Chea, Khieu Samphan, Ieng Sary and Ieng Thirith, face charges of war crimes and crimes against humanity, has been mired in delays.

Originally expected to begin hearing evidence earlier this year, it is now unlikely to get underway until 2012.

The four defendants are in their late 70s or mid-80s, but it is the health of the youngest, Ieng Thirith, that is now in question.

Experts have deemed that she is suffering from dementia and memory loss, mostly likely Alzheimer’s.

Judges will have to decide whether she will be able to cope with the rigours of a trial that is complex and will last several years.

If they declare she is unfit to stand trial, there will be protests from victims decrying the decision as justice denied.

As Nath warned in 2009: "Time is passing, please hurry up with the trial and get result. Cambodia needs to move ahead. It’s been so long."