The United Nations-backed war crimes tribunal in Cambodia has ordered the Khmer Rouge's main jailer to spend the rest of his life in prison for crimes it says were “among the worst in recorded human history.”

The ruling increased a lower court's 19-year sentence that had been appealed by prosecutors as too lenient.

The president of the court chamber, Kong Srim, said in reading the verdict that Kaing Guek Eav, better known as Duch, was a “shocking and heinous” character who deserves the “highest penalty available.”

The tribunal said Duch oversaw a “factory of death” at the feared Tuol Sleng Prison in the 1970s that was responsible for the deaths of an estimated 14,000 people.

Duch admitted his role in the crimes. But he asked for forgiveness, saying he had only followed strict orders given by senior Khmer Rouge figures.

Duch's original 35-year sentence had been reduced to 19 years for time already served in detention. That ruling outraged survivors by raising the possibility that Duch could one day walk free.

The 69-year-old Duch responded with little emotion as the verdict was read. But many survivors of the Tuol Sleng Prison, including Chum Mei, said they were satisfied with the decision.

“This is the right decision. The decision by the appeals court is right 100 percent. It brings justice 100 percent.”

National co-prosecutor Chea Leang also praised the ruling.

“Survivors who are waiting for their justice, now they get it. It is a victory for the survivors and victims and justice has been found for them.”

Hundreds of Cambodians packed the courtroom in Phnom Penh to witness the historic ruling.

The tribunal is currently trying three other senior Khmer Rouge leaders for crimes against humanity and genocide, among other charges.

It is seeking justice for the estimated 1.7 million people who died from torture, starvation, exhaustion or lack of medical care during the communist regime's rule from 1975-1979.