The investigation leading to the trial of Khmer Rouge prison chief Duch could last through April, with trials starting thereafter, a tribunal expert said Tuesday.

That means Duch, whose real name is Kaing Khek Iev, 65, could see a trial in the second half of 2008, "if there are not political or other problems acting as obstacles," said Hisham Mousar, a tribunal monitor for the rights group Adhoc.

Duch oversaw the infamous Tuol Sleng prison in Phnom Penh, where as many as 16,000 Cambodians were tortured, later to be executed in the "killing fields" outside the capital.

His trial would be the first of five jailed Khmer Rouge leaders, who were ousted from power nearly 30 years ago.

Tribunal spokesman Reach Sambath said the investigators were "expediting the investigation" and would wrap up their work by Khmer New Year, in mid-April.