A former Khmer Rouge prison chief said he used communist ideology to train guards to torture and execute prisoners.
The former jailer, known as Duch, explained his role in the prison's culture of violence during testimony Tuesday to Cambodia's genocide tribunal.
Duch, whose real name is Kaing Guek Eav, told the U.N.-backed tribunal that those who went against Khmer Rouge orders were killed.
Judges are hearing evidence about a jungle prison that Duch ran before the Khmer Rouge came to power in order to better understand later atrocities at the Tuol Sleng prison.
The tribunal is trying Duch for crimes against humanity, war crimes, murder and torture for atrocities committed at Tuol Sleng, the Khmer Rouge prison he ran from 1975 to 1979.
A former guard at the jungle prison known as M-13 described to the court how he was so afraid of Duch while under his command that he was unable to look at his face.
On Monday, another former guard told judges that he saw Duch shoot and kill his uncle at M-13 in 1974. The former guard, Chan Veoun, said he also saw Duch burn a woman's breasts with a torch. Duch said the testimony was fabricated.
On Tuesday, Duch also claimed that inhumane conditions at M-13 were due to fear of prisoners escaping or being struck by bombs dropped by U.S. B-52s. Duch said prisoners were kept shackled and hungry in two-meter deep pits to keep them "safe" and to prevent their escape.
Duch also regularly denies accusations of personally killing prisoners. However, at the start of his trial last month, he apologized for overseeing the killing of more than 15,000 people imprisoned at Tuol Sleng.
Four other former Khmer Rouge leaders are in custody awaiting prosecution by the genocide tribunal.
During the Khmer Rouge's reign from 1975 to 1979, a quarter of Cambodia's population was killed by execution squads, or died as a result of starvation and overwork.
Pol Pot, the leader of the radical communist regime, died in 1998 without facing trial.
Some information for this report was provided by AFP and AP.