Prosecutors for Cambodia's genocide tribunal are demanding a former Khmer Rouge prison chief be jailed for 40 years for his role in the deaths of thousands of Cambodians.

Kaing Guek Eav, known as Duch, expressed deep remorse in the packed courtroom in Phnom Penh Wednesday.

He apologized to the Khmer Rouge victims and their relatives, taking responsibility for the deaths of more than 12,000 people who were starved and tortured under his watch.

Prosecutor William Smith told the U.N.-backed tribunal that Duch should be held accountable for what he called the "unrelenting brutality" at the S-21 prison in Phnom Penh.

Prosecutors did not demand a life sentence because Duch has already spent time in prison, shown remorse and provided evidence against other Khmer Rouge leaders.

A ruling and sentence are not expected until early next year.  

The Khmer Rouge are blamed for the deaths of 1.7 million people during their 1975 - 1979 rule.  Some of the survivors who attended the tribunal Wednesday said Duch should face harsher punishment.

Prosecutors say Cambodians held at the prison Duch managed were routinely beaten, shocked with electricity, water-boarded and had their toenails torn out. Most died.

Duch, a born again Christian, says he never personally killed anyone and carried out his brutal work because he feared for his life.

The Khmer Rouge seized Cambodia as the U.S. was pulling out of the war in neighboring Vietnam.

The ultra-communist group emptied Cambodia's cities, killed anyone who appeared educated or elite, and forced the rest of the population to work on rural labor camps.

Some information for this report provided by AFP, AP and Reuters.