During his 77-day proceedings, Duch admitted to heading Toul Sleng, a top secret detention centre for the worst "enemies" of the state.
The 93-minute film has won 16 awards in the US and other foreign countries, including the Special Jury Prize at Sundance.
The UN-backed court is expected to release the verdict on July 26, following court proceedings that began in March 2009.
A trial is expected in March 2011.
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.