lets look at this from a slightly different angle. action and reaction.
JR undertakes little action relevant to the shooting - its all reaction.
His only action is walking around the car, calmly gathering evidence on his phone. wife says something slightly rude or offensive at him as he walks around the front of the car, with no idea of what is about to happen. at this point all this stuff about being in front of a car and protocol at traffic stops etc is all nonsense, he is not suspecting anything.
suddenly another ice escalates it to 'stop get out', and RG reverses. JR REACTS to this obvious resisting arrest by drawing his weapon to assist his fellow officer. Absolutely standard procedure.
RG drives at him. He REACTS by firing three shots in very quick succession.
That is basically it. all over in a flash. could he have reacted differently? yes. With hindsight would it be better if he had reacted differently? probably.
but officers dont get the benefit of hindsight. the actions of others mean they have to REACT in a flash. the principle responsibility for this comes from the person precipitating the action.
RG and to an extent the wife, and to an extent all the people supporting illegal obstruction of legitimate police work bear the responsibility. The blood is on your hands, not JRs.
and you love it.