The UN-backed war crimes tribunal in Cambodia ruled Friday on appeal that the former head of the communist Khmer Rouge's most infamous torture camp should serve the rest of his life in prison.

Kaing Guek Eav, better known by his alias Duch, was convicted of murder, rape and crimes against humanity in July 2010 for overseeing the deaths of at least 12,000 people when he ran the notorious Tuol Sleng Prison, codenamed S-21.

Sixty-nine-year-old Duch's original 35-year sentence had been commuted to 19 years, taking into account time served in military detention. Prosecutors then appealed the sentence, which they considered too lenient.

"The penalty must be harsh to prevent similar crimes, undoubtedly among the worst in human history," said the president of the court chamber, Kong Srim, while reading the verdict.

Duch, who converted to Christianity following the death of his wife in a 1995 burglary, had admitted his role in the atrocities and asked for forgiveness. He appealed his original sentence, claiming that it was too harsh because he only followed orders.

The purpose of the S-21 prison was to extract confessions through torture of Khmer Rouge enemies, who were then executed in the infamous "killing fields." An estimated 20,000 people were sent to S-21, with only around a dozen survivors.

The UN-backed tribunal is seeking justice for the estimated 1.7 million people who died from torture, starvation, exhaustion or lack of medical care during the Khmer Rouge's reign from 1975-1979. The Khmer Rouge was a radical Maoist movement that sought to turn Cambodia into a rural, classless society.

slk/acb (AP, dpa, Reuters)