The Khmer Rouge were overthrown over 28 years ago, on January 7th, 1979. Over 18 years later, the Cambodian government asked the United Nations to assist in the creation of a trial for the Khmer Rouge. It took another 6 years for the Cambodian government and the United Nations to come to an agreement on the structure of the tribunal, and another year for Cambodia to ratify that agreement. Two years later, on July 3, 2006, the national and international judges were sworn in, marking the start of the tribunal's efforts to get off the ground.
But justice for the Khmer Rouge has never moved quickly, and thorny obstacles soon arose. First, there was a dispute last fall between the Cambodian Bar Association and the International Bar Association over training defense lawyers, described here by Kevin Heller. Then there were allegations of corruption at the court, and lengthy negotiations over the court's internal rules that finally broke down over the bar dues dispute. The politics behind these delays are too complex to delve into here, but one can only hope that justice will finally move forward unimpeded -- and in time to meet the court's 3-year mandate.
Update: on April 30, the international judges issued a press release opining that the Cambodian Bar Association's decision to reduce proposed bar dues for foreign defense counsel should enable the court to adopt its internal rules by the last week of May. For a more detailed exploration of the history of efforts to try the Khmer Rouge, see this article by Youk Chhang, the Executive Director of the Documentation Center of Cambodia.