In a situation like that, rage and fury takes over I'm sure. Now, if he shot him moments after the crash, could that be defined as a crime of passion in law?
Since he walked home, grabbed a gun only to return and shoot him, it becomes premeditated I think.
This is a tricky one for sure and I am not sure I would not have shot him myself either in that situation. He is going to jail/prison but for how long, I have no clue.
Everyone has a plan, until they get hit.
/ Mike Tyson