Also we would expect any regular citizen to be arrested and charged in this situation. That's precisely what courts are for - to sort out whether the details are strong enough to warrant conviction. Police should not have some informal parallel justice system outside of the courts - that's the whole point.
From everything I have seen the cop was justified by law. Still a shitty situation but this smells of politics by the DA.
Edit: forgot to mention that Tennessee vs Garner established that officers have justification to use deadly force to stop someone fleeing who is a deadly danger to the public.
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.
As this is not a clear cut case of justifiable homicide, the right thing to do is let a court sort it out. If the courts are too slow and expensive, welcome to another broken aspect of the criminal justice system that is in dire need of reform!