The prison chief being tried for running a torture center for the Khmer Rouge was only following orders and did nothing that scores of colleagues didn't also do, his lawyer said Wednesday, seeking to rebut popular calls for his client to receive the maximum possible punishment.

Prosecutors in Cambodia's first genocide trial are asking for a 40-year sentence, which would likely lock up 67-year-old Kaing Guek Eav for life, but which some of his victims say that would still not be harsh enough.

Judges will decide the verdict and sentence by early next year and can impose up to life imprisonment. Cambodia has no death penalty.

"I cannot accept this sentence request because it is too little," said Chum Mey, 78, one of a handful of survivors from the S-21 prison run three decades ago by Kaing Guek Eav, also known as Duch. "He should get 70 or 80 years. ... He should be punished by hanging, but Cambodian law doesn't allow it."

Closing arguments will conclude Friday in the case of Duch, who is charged with crimes against humanity, war crimes, murder and torture. About 16,000 men, women and children suspected of disloyalty were tortured at the prison in Phnom Penh before being taken away for execution.

In total, some 1.7 million Cambodians died due to the radical communist policies of the 1975-79 Khmer Rouge regime and their French-educated leader, the late Pol Pot. Four other senior leaders are in custody, and expected to face trial in the next year.

Duch (pronounced DOIK) has denied personally killing or torturing the S-21 prisoners, and testified that he acted with reluctance on orders from his superiors, fearing for the safety of his family and himself.

Addressing the court Wednesday, he once again apologized to the dead, their families, survivors of the regime and to all Cambodians _ something he has done repeatedly since the trial began in March.

He said he was "deeply remorseful and profoundly affected by the destruction on such a mind-boggling scale."

But he also emphasized that he was not alone in carrying out torture and killings, which also took place at 196 prisons across the country, and insisted there was little he could do to prevent the horror at S-21.

"I could do nothing to help," he said. "Pol Pot regarded these people as thorns in his eyes."

One of his lawyers, Kar Savuth, said his client was not a senior Khmer Rouge leader responsible for the group's policies and therefore should not be prosecuted.

Australian co-prosecutor William Smith earlier acknowledged Duch's admissions of guilt and the fact that he has given evidence against other Khmer Rouge leaders, but said he still must be held accountable.