Trivia: Families of the 40 passengers and crew members killed on United Flight 93 cooperated in the production, offering Greengrass detailed background about their loved ones, down to the clothes they wore, what reading materials or music they had with them and what sort of candy they might have snacked on aboard the plane.
Trivia: The FAA National Operations Manager, Ben Sliney, was played by himself. September 11/2001 was also his first day on the job.
Answer: The hole where the plane went into the building is shaped very specifically where you can see the outline of the wings, the middle of the plane, not to mention its size. The holes on the other side of the building did not have this same outline. It wouldn't be difficult to determine that was the point of entry. Not to mention the CNN report focused very heavily on the point of entry hole on the north tower and hardly focused on the other sides because of it until the 2nd tower got hit. They were very clear in the report where the hole was where it got hit. Wasn't difficult to determine with both witness reports coming in fast and the shape of the outline.