I'm sure SOME are justified. I have a hard time believing that they all are or that even the majority are. Some of the reports around here eg. where a plain clothes cop shot and killed a kid because he thought the kid was driving a stolen car and didn't stop - look to me like the cop killed someone because he though he could get away with it (and he did)
I think far more often than not when the police claim that they were firing because they feared for their health and safety, or the health and safety of others then it's found to be justified. In this case, fleeing suspect known to carry firearms, the police will have no problems claiming self defense and justifying the shooting.