Corrected entry: In the opening shot of Union Square from above, all pedestrians have very long shadows. Later we learn that the action took place during the lunch hour. The sun should have been higher and the shadows shorter.
Corrected entry: Throughout the movie when Gene Hackman listens to the conversation on tape, the man says "He'd kill us if he has the chance," with no emphasis on any one word. But at the end of the film after the murder, he thinks back, and the man says "He'd kill US if he has the chance," stressing the word "us." That totally changes the significance of the sentence. If it was used throughout, it would have been easy to guess the twist at the end.