International prosecutor Andrew Cayley expected to see no more than 10 people on trial.
Reach Sambath fell in his office on Tuesday, suffering an apparent stroke from high blood pressure.
The tribunal has long been split over how many former Khmer Rouge cases it should prosecute.
The names of the accused in Case 003 have remained confidential with the court, making a petition impossible.
About 170 Cambodians survivors in the US have filed complaints with the tribunal.
The statement follows complaints by several victims of the Khmer Rouge naming those they thought responsible under cases 003 and 004.
So far the identities of suspects in cases 003 and 004 at the court have remained confidential.
Survivors were invited to draw what they could remember of the Khmer Rouge, from torture to lost family members.
The exhibition showcases 17 rare photographs taken by American photographer Al Rockoff and French photographer Roland Neveu.
Now 54, Him Huy said Monday he had been recruited as a young man the year before the capital fell.
Seng Theary filed the complaint against former Khmer Rouge commanders Meas Mut and Sous Met.
The Trial Chamber is now deciding who else among thousands of applicants will stand as witness when the trial begins.