Continuing to chase and shooting RB in the back contradicts the claim of self defense. At any time, the officer could have stopped the immediate chase and ended the confrontation. This would have been the prudent thing to do, given that they had his ID (and his car), and the two officers hadn't recovered from being overwhelmed.
This is a good example of why responding officers shouldn't carry firearms or even tasers on their person - they're too quick to keep escalating like they see on TV. If a suspect violently escapes arrest, then send in a larger armed crew with a deliberate plan.
re your addition: Seems like a decision that enables bad policing. Nothing about the situation makes it seem like RB was actually a danger to the public, but the police will push that justification all day long to legitimize what was essentially a personal ego escalation.