PHNOM PENH, Cambodia (AP) — A U.N.-backed tribunal’s Supreme Court lengthened the sentence for the Khmer Rouge’s chief jailer to life imprisonment on Friday because of his “shocking and heinous” crimes against the Cambodian people.

The surprise ruling increased a lower court’s 19-year sentence for Kaing Guek Eav, known as Duch. Prosecutors had appealed the sentence as too lenient, and outraged survivors had feared the man who oversaw the torture and killing of thousands could one day walk free.

Duch was the first defendant to be tried by the tribunal. He was commander of Phnom Penh’s top-secret Tuol Sleng prison, code-named S-21. He admitted to overseeing the torture of his prisoners before sending them for execution at the “killing fields.”

In July 2010, the tribunal’s lower court convicted Duch (pronounced DOIK) of war crimes, crimes against humanity, torture and murder.

He was sentenced to 35 years in prison but had 16 years shaved off for time served and other technicalities. The sentence was appealed both by prosecutors, who called for life imprisonment, and by Duch, who argued it was too harsh because he was merely following orders.

Judge Kong Srim, president of the Supreme Court Chamber, said Friday that the upper court felt the penalty should be more severe because the former jailer was responsible for the brutal deaths of so many.