The court has heard how Kang Guek Eav, also known as Duch, ran the S-21 death camp.
In Cambodia, the final hearings have begun in the first trial of a Khmer Rouge leader.
The court has heard how Kang Guek Eav, also known as Duch, ran the S-21 death camp. Sixteen thousand people are thought to have been held there before being executed by the Khmer Rouge government between 1975 and 1979.
Duch has pleaded no contest and given evidence that 196 such camps existed. At the camps, favorite methods of torture ranged from electric shocks and whips to water-boarding.
In their arguments representatives of S-21 victims said Duch sought to minimize his involvement as commandant of the camp throughout the trial, which began in February.
The court also heard that ultimate responsibility for the death camps rests with Nuon Chea, known as Brother Number Two, who is awaiting trial.
Human rights activist and lawyer Theary Seng says overall the tribunal has only enjoyed mixed success. Among the complaints that have been made are that the victims' representatives have too little time to speak before the court, lengthy delays in the process and allegations of corruption among the court staff.
But Theary Seng says important lessons have been learned that will be used when at least another four Khmer Rouge leaders go on trial.
"I think this first case of Duch is important in setting the momentum for the whole Khmer Rouge tribunal, after 30 years of waiting, after the politicking of negotiating the agreements after 1997," said Seng. "So it was very, very important to jump start the tribunal."
As many as two million people, or a third of the population, perished under the ultra-Maoist government - through execution, starvation or illness caused by forced moves into rural areas and overwork. The leader of the Khmer Rouge, Pol Pot, intended to turn Cambodia into an agrarian utopia.
This week, the victims' representatives, Duch's lawyers and the prosecution will deliver their final statements before the tribunal goes into recess. A verdict and sentence are not expected until early next year.
The trials of former foreign minister Ieng Sary and his wife Ieng Thirith, former head of state Khieu Samphan and Nuon Chea are not expected to begin until late 2010 or early 2011.