Continuity mistake: In Barnes' perspective, when Taylor asks him if he saw the shooter, Barnes replies, "No, but I saw something, like a flash of light." In the Howard Lewis perspective, Barnes doesn't say "No, but..." (00:17:50 - 00:36:45)
Continuity mistake: Several times when we see what's on Forest Whitaker's camcorder, the elapsed time on the bottom corner shows the same time between shots of the screen.
Continuity mistake: During the car chase scene, some of the damage Barnes's car has taken is not there in the wider shots, but you do see it in the close up shots.
Continuity mistake: At the underpass, when Taylor realizes that Barnes is right behind him on foot, he starts driving away. He's supposed to be speeding away, yet Javier, who is injured, is able to catch up to him on foot with ease.
Continuity mistake: In Barnes' perspective, when the President is shot twice, immediately after this he (the President) tilts his head to the left in response to the agony. However, in Enrique's perspective, he tilts his head right, and this isn't right, since it's the same event but from a different perspective.
Continuity mistake: In Thomas Barnes' perspective, when he confronts Enrique, he says, "Don't release him" to the other Secret Service agents. But in Enrique's perspective, Barnes says, "Do not release him." (00:17:10 - 00:27:30)
Continuity mistake: When Barnes shoots Taylor and Taylor crashes, we then see a shot of Javier on the floor, with his head on his right arm and his left arm beside it. But, when we see Barnes running to the car, Javier's body is at the lower left of the screen and his right arm has moved to his back.
Continuity mistake: This movie has a lot of problems with VWs. During the car chase, the blue car passes the red older 80's VW three times between shots. Later in the film, a blue VW rams into the turned over ambulance and in a later shot it is away from the ambulance and undamaged. In another part of the chase scene, the police car passes another blue VW two times.
Continuity mistake: When the president is abducted in the ambulance there is a shot of him waking up. In the close-up of his face as he awakes, the metal nose clamps on his plastic oxygen mask are sticking straight out; when the camera angle changes the metal flaps are clamped down on his nose.
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.
GalahadFairlight