Kaing Guek Eav has taken the stand in his trial for crimes against humanity during the Khmer Rouge regime in Cambodia.
Known as Duch, Kaing Guek Eav was the former chief of the S-21 prison where more than 14,000 people were tortured and killed.
He appeared today before the five-judge panel and calmly answered questions about his background.
He is charged with crimes against humanity in the first trial of a top Khmer Rouge official 30 years after the end of a regime blamed for 1.7m deaths.
'I have been notified of the charges against me,' the 66-year-old former maths teacher told the joint UN-Cambodian tribunal.
Duch is expected to enter a plea later this week on charges of crimes against humanity, war crimes, torture and murder.
If found guilty, he could face a maximum of life in prison in Cambodia, which has no death penalty.
The born-again Christian has expressed remorse for the S-21 victims, most of them tortured and forced to confess to spying and other crimes before they were bludgeoned to death in the 'Killing Fields' outside the Cambodian capital, Phnom Penh.
During questioning by court investigators before his trial, Duch said he was just following orders.
He is expected to be a key witness in the future trials of Nuon Chea, the regime's ex-president Khieu Samphan and Ieng Sary, its foreign minister, and his wife.
The four others have denied knowledge of any atrocities by the Khmer Rouge during its rule.