In 1997 the Cambodian Government made a formal request to the UN for international assistance in setting up a tribunal to hear cases against the senior members of the Khmer Rouge allegedly responsible for the worst crimes of the 1975-9 genocide. After lengthy negotiations, the judges were sworn in in 2006. The trials of Khmer Rouge leaders continue.
 
The trials have been held in Cambodia, with a mixture of Cambodian and international judges and lawyers. The Cambodian Government invited international participation in the process because of weaknesses in the Cambodian legal system and the gravity of the crimes being tried.
 
The commander of S-21, Kaing Guek Eav (Duch) went into hiding in 1979 but was located by journalists in 1999. On 31 July 2007, he was charged with Crimes Against Humanity. He claims that he was simply obeying higher orders when he supervised the prison and that he would have been killed had he disobeyed.
 
30 years after the fall of the Khmer Rouge, 13 years after the tribunal was first proposed and nearly three years after the court was inaugurated, Kaing Guek Eav’s trial began on 17 February 2009. On 26 July 2010, Kaing Guek Eav was found guilty of Crimes Against Humanity and sentenced to 35 years in prison. After an appeal by prosecutors, the Supreme Court Chamber increased his sentence to life imprisonment on 3 February 2012. The decision is final and cannot be appealed.
 
In 2011, three of the most senior Khmer Rouge officials – Nuon Chea, Ieng Sary, Ieng Thirith and Khieu Samphan began trial for Crimes Against Humanity. Since then Ieng Thirith has been found unfit to face trial. Ieng Sary died in March 2013. The cases against Nuon Chea and Khieu Samphan continue.