Khmer Rouge tribunal judge Ney Thol, who is also the head of the military courts that detained accused torture chief Duch for nearly nine years without trial, has withdrawn himself from Duch's first tribunal hearing, scheduled for later this month.

Ney Thol will be replaced by Pen Pichsaly, as a panel of tribunal judges determines whether Duch, whose real name is Kaing Khek Iev, can be released ahead of his trial, tribunal spokesman Reach Sambath said.

Ney Thol withdrew because of his position in the military courts, Reach Sambath said. Duch faces charges of crimes against humanity for his role as the head of the Tuol Sleng prison, where up to 16,000 Cambodians were tortured and later executed. He was arrested in 1999 and was held by the military courts without trial until he was handed over to the tribunal, which charged him and detained him earlier this year.

Duch's lawyers have said his excessive detention without trial should be grounds for pre-trial release.

Legal expert Hisham Mousar, who monitors the tribunal for the rights group Adhoc, said the courts should be careful in swapping judges in the middle of procedures.

"Now the pre-trial chambers are in the process of hearing Duch's appeal, so it could be very suspicious when one judge resigns and is replaced by another," he said. "The suspicion could either be about the court's independence or the court's technical issues."

Khmer Rouge tribunal prosecutors, meanwhile, began a series of meetings Wednesday with other international tribunal experts, to help them prepare for upcoming trials.

A group of prosecutors from four atrocity crimes tribunals, from the former Yugoslavia, Rwanda and Sierra Leone, met Khmer Rouge tribunal prosecutors for two days of meetings.

"As a result of our own experiences, we have some of the best practices, which we can share with the Cambodian tribunal," said Hassan Jallow, who was a prosecutor in Rwanda's genocide tribunal. "For instance, how to investigate specific kinds of offences related to sexual violence, how to handle witnesses, how to deal with confidential sources [and] what measures to take in order to make sure the cases move much faster."

"We are going to use the results of this discussion to bring to justice those responsible for fundamental human rights violation," Cambodian prosecuting judge Chea Leang said. "This exchange of ideas and experiences will improve the quality of the trial and bring about justice to the world."