Observers say the tribunal risks losing its legitimacy if its objectivity is compromised by politics.
The award-winning Khmer Rouge documentary “Enemies of the People” is expected to be shown in Cambodia in July.
Sean Visoth requested leave for health reasons in November 2008, as international donors were considering corruption allegations.
The film also won prizes at the Sundance Film Festival earlier this year.
The UN-backed Khmer Rouge tribunal is in the midst of investigating its second case of former regime leaders.
Heather Ryan, a tribunal monitor for the Open Society Justice Initiative, talks about the current financial strains faced by the court.
Donors pledged about $17 million for expenses in 2010, money far short of the $85 million that they need for 2010 and 2011.
A judge says an investigation into further cases cannot take place until the court deals with its second trial.
The Cambodian side of the hybrid court is facing dire economic circumstances, with staff salaries halved in April.
The Khmer Rouge tribunal verdict for Kaing Kek Iev, the torture chief better known as Duch, will be announced July 26.
In Cambodia, May 20 is known as the Day of Anger.
The delegation of four will assist in a pledge meeting on May 25 to solicit promises of funding from donor countries.