Andrew Cayley, in an interview with VOA Khmer, addresses concerns in Case 003 and 004, following his lecture at Rutgers University.
Filmmaker Thet Sambath said his work has contributed a small part to the Khmer Rouge history.
Thet Sambath and co-producer Rob Lemkin answered questions from nearly 50 people in the audience after the film.
Prime Minister Hun Sen and other top officials have repeatedly said in public statements they do not want the cases going forward.
The court is preparing for its biggest trial to date, for four jailed regime leaders, but it has faced a rash of criticism in recent mon
Tribunal officials have told local media that edits to court documents is a regular occurrence and not improper.
Prosecutors say the five suspects in cases 003 and 004 were close enough to the leadership of the regime to be investigated.
Neither suspect is willing to speak to reporters, according to friends and neighbors in Battambang province, where they both keep homes.
The complaint follows the resignation earlier this month of UN investigating judge Siegfriend Blunk.
Patricia O’Brien, UN undersecretary-general for legal affairs, met with Cambodian officials to discuss concerns for the tribunal.
A growing number of court observers now say the court’s approach to cases 003 and 004 is derailing its credibility.
Medical experts said her current mental state would prevent her from fully participating in a trial, even by video link.