Arthur could of easily just kept that gun as a memento to Sutherland's character. He obviously cared about him a lot too so why is it so crazy to think maybe he just wanted to keep it? Ya he shot the gun at the car and then Arthur shot him with it but there's no way forensics could clarify that it was indeed his own gun that those shots belonged to.
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SPOILER ALERT
SPOILER ALERT
I don't think he was 100% sure Arthur did it until he started asking Arthur questions like "Have you ever killed someone you know?" etc. Now, obviously anyone could argue that Foster's character still didn't have enough proof, but this movie had too many loose ends to dwell on just this one.
Nah-calling it your job don't make it right, Boss.
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I think he suspected him early on. How else would his dad be killed like a sitting duck unless he was lured there by someone he trusted? The son must have known the carjacking cover story was crap. I think he knew Arthur would probably stop him from killing the random carjacker. The gun sealed the deal.
shareAgreed. Also, Steve might've also had his suspicions confirmed when Arthur conceded to train him, considering that he's totally not the type to do something like that. I don't remember exactly, but I vaguely recall Steve initially insinuating that Arthur owed him, because instead of training his own son, his father passed on his skills to Arthur instead. Arthur felt a tiny bit sorry for Steve and seeing how he's not the kind of person to feel remorse for his assignments, I'm sure Steve took his "generosity" as another sign of guilt for killing his father.
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