The national and international lawyers have said they are skeptical about the interpretation of the laws governing the tribunal.
The ceremony will include prayers and will allow participants to lay wreaths at the 'killing fields', Cheoung Ek graves.
Investigating judges have been criticized for hastily concluded Case 003, without field investigations into some sites.
The defendants in this case, the court’s second, deny all charges.
The Khmer Rouge Tribunal is caught up in a spat between its investigating judges and international prosecutor over case 003.
The Trial Chamber expects to review more than 1,000 witnesses, experts and civil party applicants for the trial, known as Case 002.
Seng Theary announced Monday she plans to apply as a civil party for the Khmer Rouge tribunal’s Case 004.
The handling of case 003, which the government opposes, has set off a raft of complaints from victims groups and legal experts.
It remains unclear under what authority the court would
pursue such action.
Court observers say the statement from OSJI and the submission of Cayley do not necessarily signal a problem at the court.
The UN-backed court’s investigating judges have come under fire in recent weeks after they made a preliminary conclusion to Case 003.
At least five key staff members have left the Khmer Rouge tribunal’s investigating judges’ office since April.