Tribunal prosecutors have sent their final charges, documents and evidence to the investigating judges in the case of Kaing Kek Eav, alias Duch, paving the way for the first trial of five jailed Khmer Rouge leaders.

Duch faces charges of crimes against humanity, grave breaches of the Geneva Conventions, and crimes of torture and homicide. He was the chief of Tuol Sleng prison, where as many as 16,000 Cambodians were tortured and sent to their deaths.

A closing order must now be issued by the investigating judges, which will comprise the full indictment of the former Khmer Rouge cadre.

The prosecutors submitted documents related to interviews with 63 witnesses, including ex-guards and victims, investigations of 25 alleged crime locations and 27 interviews with Duch, tribunal prosecutors said in a statement.

Observers said the submission will bring about a trial date very soon, more than two years after the hybrid tribunal began.

"I believe that it would take one to three months to begin," said Long Panhavuth, a tribunal observer for the Open Society Justice Institute.

Hisham Mousar, a tribunal monitor for the rights group Adhoc, agreed with the timeframe, but said investigating judges will need to collect documents from both the defense and civil parties first.

"It would take two or three weeks' time," he said. "We can see all the documents sent to the co-investigating judges and then sent to the Trial Cahmber judges to make a date."