When James Stewart hear the scream (where Raymond Burr supposedly kills his wife) the courtyard is quiet and when the camera shows a wide shot of the courtyard you don't see anyone on the street (although a car goes by) shown on the left side of the building across the way. A few minutes later Raymond Burr leaves his apartment and when he walks down the street you see two other people walking and a few people in the bar across the street where the piano is playing, although it's almost 2am (James Stewart checks his watch)and it's raining. When Raymond Burr returns about half an hour later the street is empty and quiet again.