Writer and director Paul Greengrass relied on interviews with the families of those aboard United 93 in order to successfully re-create what happened that morning. Although no one will ever know what exactly happened on board United 93, Greengrass does a fine job of using what he has recorded from interviews and tapes from the plane to re-create closely what probably occurred. In order to present an accurate portrait of how the passengers might have reacted to what was happening, Greengrass chose “real people” rather than professional actors to play the parts of the passengers, and, further enhancing the realism, important figures such as Ben Sliney, head of the National Air Control Center, played themselves. Moreover, to give a sharp edge to the fight scenes on board the plane, the actors who played the hijackers and the actors who played the passengers were strangers -- Greengrass did not introduce them to each other beforehand. One last important example of Greengrass’s care to replicate the events as scrupulously as possible in his original script is the fact that the movie largely progresses in “real time,” nearly exactly paralleling the times of events on the morning of September 11, 2001.