Kaing Guek Eav, better known as Duch, who oversaw deaths of 15,000 people in 1970s, has sentence increased after appeal.

A former Khmer Rouge jailer who oversaw the deaths of about 15,000 people will spend the rest of his life in jail, Cambodia’s UN-backed court has ruled in a final appeal verdict.

“The Supreme Court Chamber decides to impose a sentence of life imprisonment against Kaing Guek Eav,” said Kong Srim, president of the court’s highest appeal body, on Friday.

Kaing Guek Eav, better known as Duch, was sentenced to 30 years imprisonment in 2010 for crimes against humanity, and war crimes, over the torture and deaths of thousands of people at the notorious S-21 prison in the late 1970s.

“The crimes by Kaing Guek Eav were undoubtedly among the worst in recorded human history. They deserve the highest penalty available,” Kong Srim said.

Led by Pol Pot, who died in 1998, the Khmer Rouge was responsible for what has become known as Cambodia’s “killing fields”, which wiped out nearly a quarter of Cambodia’s population through starvation, overwork and execution.

Clair Duffy, a human rights lawyer who is monitoring the prosecutions, told Al Jazeera that Duch’s sentence could prove problematic according to the law.

“Duch had been illegally detained by Cambodian military authorities for eight years, so the trial court actually gave him a five year reduction in his sentence in recognition of that fundamental violation of his rights, and today that was overturned by the majority of the judges on the appeals court,” she said.

“Ultimately, this is a court of law that is supposed to be applying international standards. This is not the Cambodian public putting Duch on trial here. These are judges who are not supposed to be swayed by public perception.”

Al Jazeera’s Stephanie Scawen, reporting from outside the court in Phnom Penh, described some of the atrocities committed at S-21 prison: “Bloodletting was quite common… Others had their hands tied behind their backs and were strung up on exercise bars. When they went unconscious they would be dunked in water, and the process was started again. It was a horrendous regime.

“The court was very strong in repeating the gravity of the crimes that he committed,” she said.

‘Following orders’

S-21, also known as Tuol Sleng, was the centre of the Khmer Rouge security apparatus and thousands of inmates were taken from there for execution in a nearby orchard that served as a “killing field”.

Duch, 69, was the first Khmer Rouge cadre to face the international tribunal.

His trial attracted huge interest in a nation still haunted by the brutality of the regime, blamed for the deaths of up to two million people.

During his nine-month trial, Duch repeatedly apologised for his role at S-21, but surprised the court by asking to be acquitted at the 11th hour.

On appeal, Duch told judges that he only survived because he “respectfully and strictly followed the orders”, while his lawyers argued that their client should be released because he was “just a minor secretary”.

Prosecutors said the shock request for a full acquittal showed Duch lacks remorse and demanded a life term, to be commuted to 45 years for time spent in unlawful detention before the court was established.

Duch has been held in detention since he was found working as a Christian aid worker in the Cambodian jungle in 1999. He was formally arrested by the tribunal in July 2007.

A second trial involving the regime’s three most senior surviving leaders opened at the court late last year, but there are fears that not all of the defendants, who are in their eighties, will live to see a verdict.

They are 85-year-old Nuon Chea, the Khmer Rouge’s chief ideologist and second in command; 80-year-old Khieu Samphan, an ex-head of state; and 86-year-old Ieng Sary, the former foreign minister.

They are accused of crimes against humanity, genocide, religious persecution, homicide and torture, and each claim no wrongdoing.