Character mistake: At the end of the film, the newscaster comments that the lone assassin has been killed, but the ticker beneath him reads "Lone assassin arrested."
Character mistake: When Barnes is trying to describe what he saw, he awkwardly describes "something like a flash of light." A Secret Service agent would know that he had seen the muzzle flash from the gunshots. (00:17:40)
Character mistake: After Barnes rescues the President, he radios in his location as "seven blocks east of the plaza." This is meaningless on the limited-access highway where they are located. Barnes has an excellent grasp of the local geography and would give their precise location with specific landmarks. (01:21:20)
Character mistake: At the end of the movie the reporter says the lone assassin was shot and killed but the banner at the bottom says the lone assassin was arrested.
Character mistake: While talking to President Ashton, Phil McCollough comments, "We're looking for five people out of six million." Salamanca's population is only about 160,000.
Answer: He assumed by the movement of the curtains that there must be someone up there, which of course the Secret Service should have cleared to make sure there was no-one there.
GalahadFairlight