Vann Nath, who survived the notorious Tuol Sleng prison by painting portraits of Pol Pot, died yesterday afternoon at a private clinic in Phnom Penh at the age of 66.

The well-known artist passed away at about 12:45pm, Lon Nara, his son-in-law said. Vann Nath lapsed into a coma last week after suffering a cardiac arrest, and had been receiving urgent care treatment at La Sante Hemodialysis centre.

“I have lost my father,” Lon Nara said. “But it is lucky for him because he will not suffer in his heart anymore. When he was living, he was tortured every day by his memory.”

Vann Nath was one of a handful of known living survivors of S-21, where perhaps 14,000 people were sent to their death under the Khmer Rouge. He was the first survivor to give witness testimony in June, 2009 during the trial of the prison’s chief, Kaing Guek Eav, better known as Duch.

Bou Meng, who also survived S-21 with Vann Nath, said he regretted that his friend would not live to see the Khmer Rouge tribunal’s final judgment in Duch’s case.

Duch was convicted of crimes against humanity and grave breaches of the Geneva Conventions last year, but the court is still considering appeals against the verdict and sentence.

Youk Chhang, director of the Documentation Centre of Cambodia, said Vann Nath was a “witness to history”.

“As one of only 14 known survivors of the infamous Tuol Sleng S-21 prison, Vann Nath was a witness to history and exhibited great strength in providing his testimony despite the horrific crimes he suffered and in the face of the impunity enjoyed by his former tormentors for over thirty years,” Youk Chhang said.

Vann Nath has called his own story “surreal”, distinctly aware of the irony that aided his survival as an artist. “As for those who escaped death, they were deprived of all rights and even emotions, sculpted to serve as the tools of the rulers,” he wrote in his 1998 memoir, A Cambodian Prison Portrait.

Vann Nath was born in Battambang city in 1946 to a family of farmers. He became an artist and, in the late 1960s, set up a small business in Battambang where he sold cinema placards, individual portraits and billboards of King Father Norodom Sihanouk.

He farmed with his family under the Khmer Rouge in Norea commune, in Battambang’s Sangke district, until he was told on December 30, 1977 that he would be sent to Pursat. Instead, he was accused of murder and interned at Wat Samrong, where he was interrogated in a room with “blood spots everywhere”. He was electrocuted until he lost consciousness.

About a week later, he was taken in a lorry to Tuol Sleng.

There, he endured “indescribable” conditions for about a month, before he was taken to meet Duch, who asked him to paint a replica of a photograph of Pol Pot. Duch found his paintings acceptable, allowing him to live until the Vietnamese invasion of Cambodia in 1979.

Perhaps incredibly, Vann Nath returned to Tuol Sleng in 1979 to paint harrowing scenes of torture and conditions at the prison, which he helped open as a genocide museum in 1980. His paintings remain at Tuol Sleng today.

When asked during the Duch hearings in 2009 by Trial Chamber President Nil Nonn why it was important to him to testify, Vann Nath said he wanted younger generations to learn from the Khmer Rouge period.

“I determined if one day I survived and had freedom… I would compile the events to reflect on what happened so that the younger generation knew – would know of our suffering,” he said. “So I had to reveal, I had to write, I had to compile, and it can be served as a mirror to reflect to the younger generation of the lives of those who were accused with no reason, who committed no wrong, and that they were punished that way. That was the very suffering that we received and the suffering that we had because we told them the truth and they did not believe it.”

Vann Nath is survived by his wife, two daughters and son. A Buddhist ceremony will be held to remember his life today.