THE chief torturer under the Khmer Rouge "Killing Fields" regime wept and prayed today as he led the judges who will try him for crimes against humanity around the mass graves for some of its victims.

Duch, also known as Kaing Guek Eav, accompanied 80 judges, lawyers and other officials of a UN-backed tribunal to the 129 graves, uncovered after a Vietnamese invasion sent the Khmer Rouge back to the jungles in 1979.

"I saw Duch kneel in front of the trees where Khmer Rouge soldiers smashed children to death," a policeman said after the four-hour tour.

"He cried and apologised to the victims" in the former ricefields outside Phnom Penh, he said.

Stacks of excavated skulls mark the area.

Detained in 1999 and now a Christian, Duch is expected to be a key witness in the trials of "Brother Number Two" Nuon Chea, Khmer Rouge leader Pol Pot's right hand man, Khieu Samphan, president under the regime, Ieng Sary, its foreign minister, and his wife.

The defendants face a maximum of life in prison.