PARK CITY (AFP) - While Hollywood-style Osama bin Laden manhunt movie "Zero Dark Thirty" has garnered controversy and awards, a lower-profile film seeks to tell the real story of finding the Al Qaeda chief.

"Manhunt," a documentary by US director Greg Barker, was presented at the Sundance Film Festival this week, days after Oscar-winner Kathryn Bigelow's dramatisation won best actress Golden Globe for Jessica Chastain.

In meticulous detail, including through interviews with ex CIA agents, it traces the two-decade hunt - one before 9/11 and one after - that led to the Abbottabad, Pakistan hideout where Bin Laden was killed on May 1, 2011.

The film, produced by American television channel HBO, is one of the most highly-anticipated at America's biggest independent movie festival in the snowy mountains of Utah.

Barker began working on it shortly after the Abbottabad raid, and knew that Hollywood was already working on a dramatised version. "I was aware they were doing the film, but there was no contact whatsoever. I kept this project very quiet, because of all the controversies around that movie going way back," he told a small group of journalists at Sundance. "I just thought the less I say about what we are doing, the better."

"Zero Dark Thirty" - which is up for five Oscars next month - was accused before its release in December of being effectively a propaganda coup for President Barack Obama, who was facing re-election last year.

No sooner had it hit the screens than it drew a barrage of criticism from the CIA, outraged at the graphic depiction of torture and its key role in providing the intelligence which led to Bin Laden. For Barker's documentary, three CIA agents who appear in the film turned out to help promote it in Sundance - and shared their far-from-glowing opinions on Bigelow's movie. "That was fun to watch," said former agent Cindy Storer, while her colleague Marty Martin echoed: "As a piece of entertainment, I enjoyed it."

Martin added: "Anytime you're taking an event that we know is fact and you're making entertainment, you know that there's going to be some interpretations and perceptions there." But he said: "There are some errors in the movie and of course you relate with it, because you know the personalities.

"The obvious one, the most egregious that made us sad is the depiction of our colleague Jennifer Matthews who died in the Khost bombing," he said, referring to the 2009 attack on an Afghan base which killed seven CIA agents. “That character as portrayed in the movie was not her. She was much more serious. It was a misrepresentation of her personnality, her demeanor and the way she operates."

On the Hollywood movie's depiction of torture, the three ex CIA agents are unanimous.