But on Friday survivor Theary Seng, whose parents were both killed during the Khmer Rouge's 1975-79 rule, asked the UN-backed tribunal to reject his request, saying he may seek to evade justice .
Nuon Chea is the most senior living leader of the Khmer Rouge and is accused of being the architect of the policies that led to the deaths of some 1.7 million Cambodians.
He sat impassively as Theary Seng and two lawyers representing other Cambodian victims spoke.
"We have been waiting for 30 years for justice"
Theary Seng, Khmer Rouge survivor
"As victims, we have been waiting for 30 years for justice," Theary Seng, a Cambodian-American lawyer who survived the atrocities as a child, told the pre-trial hearing.
"There is a risk that the accused will fail to appear in court, and without his presence we will suffer a great loss."
Theary Seng, who was jailed when she was seven, said Nuon Chea and the Khmer Rouge had been totally merciless.
|Survivors of the Khmer Rouge have waited |
more than three decades for justice [EPA]
"My brother, who was younger than me, and I were put in prison under Mr Nuon Chea's regime. We were not informed of our rights," she said, noting the irony of him being given full protection under domestic and international laws.
"There was no due process and we were arrested arbitrarily. They treated us inhumanely – for us, the graveyard was our playground."
Helen Jarvis, the tribunal spokeswoman, described Theary Seng's appearance as "historic".
"To actually stand across the room from someone who a victim feels is responsible for their suffering is very important and at the leading edge of international justice," she told AFP.
Nuon Chea, who was arrested last September, is one of five former Khmer Rouge leaders awaiting trial before the UN-backed tribunal, expected to start formal trials later this year.
The chief ideologue to Pol Pot, the notorious Khmer Rouge leader, denies guilt and calls himself "a patriot".
He surrendered to the Cambodian government in 1998 and was given a formal pardon allowing him to live freely in the western border town of Pailin until he was arrested and brought before the tribunal last year.