Mike Irwin pointed out correctly that in this case, it seems that two (2) crimes were committed by the deceased. First was armed robbery of the woman and the second was ADW - by threatening the "good Samaritan" with a firearm.
It appears that during the robbery the perp display and used a firearm so if the pursuing citizen had already drawn his gun we can see two possible lines of thought there.
Police / Armed Citizen: A prudent move in case the perp uses his firearm instead of surrendering or dropping the stolen property.
Politicians / D.A.'s: A clear indication of the citizen's vigilantism and intent to take the law into his own hands.¹
This is one reason why I will rarely, if ever pursue. A simple difference of viewpoint may be the difference between accolades or felony indictments. But being the kind of person I am, I'd have a hard time simply walking or driving by while someone is getting the short end of the stick. At the very least, we owe it to each other to assist in the immediate aftermath with first aid, calling police and being good witnesses.
¹ Law enforcement begins and ends with the citizenry. If armed citizens won't help enforce the laws when feasible then the laws lose significant effectiveness (as we've seen). Citizens apprehending the criminals happens every day and it improves community safety. Politicians and public officials who discourage citizens from aiding their communities ultimately seek to let crime flourish for their own gain.
BillCA in CA (Unfortunately)