Who knows why he was running? Maybe he didn't want to get tased?
Who knows why a cop entered his life in the first place?
Those questions are fine and dandy, but take away from the far BIGGER question.
Why did a cop fire his weapon 8 times in the back at a man who was fleeing from him? Why did the cop attempt to manipulate the crime scene? Why did the cop not even try to track him down? Call for backup?
It seems like you're trying to be one of those "must have been doing something wrong type of guys." Which really detracts from the fact that this man was murdered by someone who is being paid by taxpayer dollars to serve.
Did the cop pick him out to kill for fun? Unlikely. Who knows? What are you basing that on anyways? Do you know the cop? Do you know anything about him? Did the cop have fun while he clearly murdered the man? I don't know.