Question: What would've happened if Sonny drove the limo himself, refused to tell the police where they were going, and told the police not to follow them? Also, if Sal had hostages sitting behind him as well, making it impossible for the police to get a clean shot? How could the police have stopped them, without getting any hostages killed?
Question: What if in the middle of the robbery, while Sonny was outside, he suddenly decided he wanted to surrender, while Sal was still in the bank, and didn't want to surrender? What would the police have done? Arresting him would've likely got the hostages killed, but they couldn't force him to go back in the bank.
Question: How did Sonny know that the black limo driver was a cop?