As to Bobby's dropping the gun at the scene of the crime: To me that was one of two homages to The Godfather. Remember when Michael Corleone kills Solozzo and McCloskey (the cop) in the Italian restaurant. He's gotten instructions to drop the gun from Clemenza. There's no problem as long as the gun's clean. The second homage, IMO, was when Tony was sitting in the chair looking at the lake. Janice even says, "I've seen this before." Yeah, in Godfather II, when Michael Corleone is sitting looking out at the lake thinking of his brother Fredo that he had killed.