Duch, centre, surrounded by pictures of his victims

Two of them are already in custody - Ta Mok, nicknamed "The Butcher", a brutal regional commander, and the man known as Duch, who ran the notorious Tuol Sleng torture centre where thousands were killed.

But others are still at liberty and there are doubts over whether they will ever be brought before the tribunal.

Two of the top Khmer Rouge leaders, Nuon Chea and Khieu Samphan live in Pailin, the one-time jungle headquarters of the movement when it was fighting the Hun Sen government.

Ta Mok: "The Butcher"

Both deny knowing anything about the killings and atrocities that went on, but documents prepared by human rights researchers suggest that at the very least they were fully informed.

Another leader, Ieng Sary, the former Khmer Rouge foreign minister, is more problematic, because he was given an amnesty by King Sihanouk in 1996 when he agreed to surrender with some of the Khmer Rouge forces.

Civil war fears

The United Nations says such an amnesty cannot protect someone from prosecution by the special tribunal, but Cambodian Prime Minister Hun Sen has warned that going after Ieng Sary could reignite a civil war in Cambodia.

Ieng Sary has close links with China, which was the Khmer Rouge's main backer, and the Chinese Government still opposes the tribunal.

Even if indictments are issued against the surviving members of the Khmer Rouge, the tribunal will have to move quickly - many of them are old and in poor health.

Like their leader Pol Pot, they may not live long enough to answer for their roles in Cambodia's gruesome past.