Your characterization of the recent killing of Mr. Brooks is incomplete. Brooks fought against the police and fired a taser (a deadly weapon according to the Atlanta DA) at the officers giving him chase. They were absolutely justified in shooting him.
The problem we have in America is that many people think it's ok to fight the police. Almost all publicized police killings in recent years are a result of suspects resisting arrest in a violent manner, escalating things to the point where force is required to control them. Of course this doesn't fit the narrative, so it's ignored.