Jessica Chastain

The actress read "book upon book" to prepare for her role in controversial new film 'Zero Dark Thirty', Oscar-winning director Kathryn Bigelow's movie about the covert operation to kill the al-Quaeda founder.

The actress plays CIA agent Jen, who had a crucial role in tracking bin Laden to a compound in Abottabad, Pakistan, where he was killed on May 2nd, 2011.

Jessica said: "We did extensive research. Books upon books. I read [Lawrence Wright's] 'The Looming Towers', I read Michael Scheuer's book on Osama bin Laden. I got to know my subject inside out."

The film has been shrouded in secrecy, with those involved - including the film's stars, director and writer Mark Boal - reluctant to give away too many details. Jessica says this is because of contributions from real people involved in the operation.

She told GQ magazine: "I did talk to a lot of people but I don't really want to specify to whom I spoke.

"The reason they're trying to keep so much of it a secret is because there are so many people involved - real lives."

Here's the trailer for "Zero Dark Thirty":