Up to two million Cambodians are thought to have died or starvation or execution during the Khmer Rouge's brutal four-year rule.
The group's leader, Pol Pot, known as Brother Number One, died in his jungle hide-out in 1998 without ever being brought to justice.
Khieu Samphan, now 76, was the public head of the Khmer Rogue organisation
He was Cambodia's head of state from 1976 until the ousting of the Khmer Rogue by Vietnamese forces in 1979
The son of a judge, he studied for a doctorate in economics at the prestigious Sorbonne in Paris
After surrendering to the government in 1988, he was arrested on November 19, 2007, at a Phnom Penh hospital where he was being treated for a stroke
Has authored two books in which he denies claims of mass killings by the Khmer Rogue and says Pol Pot was responsible for all policies
Duch, the former boss of the notorious Tuol Sleng detention centre, and Iengy Sary, Pol Pot's deputy, are both awaiting trial and have both had appeals for bail rejected.
The tribunal is expected to hold its first trial later this year.
Appearing in court on Wednesday Khieu Samphan said he had lived a very simple life since deserting Cambodia's once notorious regime 10 years ago.
"I've had no job since leaving the jungle. I have only my wife, who struggles to feed me and my family," he told the judges.
In its detention order, the tribunal alleged that Khieu Samphan "aided and abetted'' Khmer Rouge government policies that it said were "characterised by murder, extermination, imprisonment, persecution on political grounds and other inhumane acts".
Blaming Pol Pot
Khieu Samphan, in various public statements made before he was arrested, has blamed Pol Pot for the group's policies saying he had no real power in the Khmer Rouge.
Among the legal team representing Khieu Samphan is Jacques Verges, a French lawyer who has earned notoriety for representing accused terrorists, serial killers and a former Nazi officer accused of World War II atrocities.
His former clients include notorious hijacker Carlos the Jackal; Slobodan Milosevic, the former Yugoslav President; and Nazi Gestapo officer Klaus Barbie.
|French lawyer Jacques Verges has joined |
Khieu Samphan's defencce team [EPA]
Verges, who is 83, has known Khieu Samphan since they were both active in left-wing student activities in Paris in the 1950s.
He is expected to use a more aggressive approach than other lawyers at the tribunal have so far employed.
Say Bory, Khieu Samphan's Cambodian lawyer, said on Tuesday that the
tribunal's decision to hold the hearing behind closed doors was "regrettable" because his client "desired to speak for the public to hear him".
Khieu Samphan himself has never denied the bloodshed suffered by the Cambodian people.
But in an interview in 2003, he urged Cambodians to let go of the past, saying: "We have much more problems to resolve at present and in the future, and we have to forget the past."