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Revealing mistake: During the struggle in the elevator, the pistol discharged three times into the ceiling (covered light) but no fragments fell. A little later when the whole ceiling is shown, the ceiling is not damaged and there aren't any signs of bullet holes. (01:04:35 - 01:05:12)

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Revealing mistake: Interior versus exterior views of the window sill/ledge are different when Brandon is aiming his rifle out. From inside the building, the window sill looks flat and the front tripod legs are close to the inside; from outside the window, the front tripod legs are over the window frame plus the ledge is layered. In some shots, it also looks like the window pane was opened horizontally to the left, but Brandon opened it by pushing it vertically upward to overlap the top pane. (01:00:43 - 01:01:41)

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