The Khmer Rouge prison chief was "shocked" when  confronted with his bloody past and has prayed for forgiveness, he told Cambodia's UN-backed war crimes trial Tuesday.

Kaing Guek Eav, better known as Duch, is on trial for overseeing the torture and extermination of 15,000 people. They passed through the hard line communist movement's notorious Tuol Sleng prison, also known as S-21.
 
"When I arrived at S-21, I was shocked for the numerous things that happened there. I saw three victims or survivors, who stood before me. What happened in the past came back into my mind," Duch said.
 
The 66-year-old describes his visit with court investigators last year to the former prison so that he could re-enact his crimes. The prison now serves as a genocide museum.
 
Duch's defence team proceeded to show a short video of the visit, in which he attempts to speak but begins to sob uncontrollably, removes his glasses and is comforted by his lawyer.
 
"I made a speech for the souls of those who died. This is something that I can never forget, the trip to killing field Choeung Ek and S-21 in Phnom Penh," Duch said.

He told the court he became consumed with sorrow after fleeing the prison in the face of Vietnam's 1979 invasion of Cambodia, and began to pray.

Earlier in the day, Duch told the court he was twice incriminated in written confessions by prisoners interrogated at his jail, and both times he left the text for his superiors to see  hoping that his loyalty would save him.
 
"I did not make any changes to it because if I did, people would notice that I deleted my name because I did not want to be implicated," Duch said.
 
Swiss lawyer Alain Werner asked the former prisoner chief how he then avoided being interrogated and executed, which was standard practice for those named in confessions during the 1975-1979 regime.
 
"Why did nothing happen to you even though you were implicated twice in confessions? Was it because you were protected by your superiors... who admired your zeal?" Werner said.
 
Duch answered that the confessions, by a purged superior and a former teacher, were not particularly strong, but added: "The fact is I survived because I insisted I was loyal to Khmer Rouge leaders."
 
As his trial for war crimes and crimes against humanity began in March, the former maths teacher begged forgiveness from the victims of the movement and accepted responsibility for his role at Tuol Sleng.