""We went to great lengths to make sure that their identities wouldn't be in any way jeopardised by the film. We made sure not to cast actors who bore physical resemblances to the people... A lot of these people are still working. We take protecting those people very seriously."" Screenwriter Mark Boal on the caution taken in casting stars for his new movie Zero Dark Thirty, which chronicles the real-life hunt for terrorist leader Osama bin Laden. He was killed by the U.S. military in Pakistan in May, 2011.