Prosecutors of the first Khmer Rouge commander to face a UN-backed trial have appealed against his prison sentence for being too lenient. They claim that “undue weight” was placed on mitigating circumstances.

Judges in the trial chamber of the Extraordinary Chambers in the Courts of Cambodia (ECCC) found Kaing Guek Eav guilty of murder, torture, rape, crimes against humanity and other charges as chief of S-21 camp in the 1970s. The 67-year-old, also known as Comrade Duch, oversaw up to 14,000 deaths in Cambodia. In a statement prosecutors said:

“Prosecutors are of the view that the judgement gives insufficient weight to the gravity of Duch’s crimes and his role and his willing participation in those crimes.”

Duch was jailed for 35 years at the end of July, but he is likely to face just half of that as a result of time already served and compensation for a period of illegal detention by the Cambodian Military court between 1999 and 2007.

Between 1975 and 1979 around 1.7 million people went to their deaths in Cambodia’s notorious “killing fields.” Duch told the court that he had no choice but to carry out orders and “kill or be killed.” But prosecutors insisted that he was “ideologically of the same mind” as the Khmer Rouge’s top leaders and that he did nothing to stop the rampant torture at his prison, also known as Tuol Sleng.

The joint UN-Cambodian court spent more that 78 million dollars over five years to bring the first of five indicted Khmer Rouge officials to trial.

In its verdict on July 26 the court decided against a sentence of life in prison because Duch had shown remorse and because of his “potential for rehabilitation”.

In a separate development, prosecutors have requested that the ECCC formally indicts four senior figures under the Khmer Rouge. Nuon Chea, Ieng Sary, Khieu Samphan and Ieng Thirith are accused of crimes of genocide, crimes against humanity, grave breaches of the Geneva Conventions and violations of the 1956 Cambodian penal code.