>Why did they shoot him?
Because they had already made the determination before the gun was fired.
>Was he an imminent and deadly threat to them?
no
after they pursued him in their truck with their guns.
3 vs 1
wouldn't you make the attempt to take a gun if you were out numbered?
Sounds like a good idea except for… it will be the American taxpayer that will be on the hook for the payouts.
Disbanding the FBI and preventing any of them from (self) serving in government - local, state or federal for the rest of their lives would be a much better and longer lasting outcome.