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.
Continuity mistake: When the US Secret Service agents take the Spanish Police agent into custody before the explosion, the agent takes the Spanish Police agent's police badge off his belt and hands it to another US Secret Service agent. After the explosion the Spanish Police agent is seen running away from scene and his police badge is shown back on his belt. (00:27:00 - 00:30:00)
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.
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