How is suspene created in the film you watched in class?

In class we watched the film United 93 which is based on the 9/11 attacks. Suspense was created through the editing as they would cut from one scene to another at various times to keep to you on edge of each scene. Also at the start of the film as the camera showed us New York City there was a voice over from the terrorist which kept us wondering what was going to happen in the film. As well as that before the terrorist hijacked the plane they looked uncertain about doing it and kept us waiting which kept us on edge in suspense about what would happen.