He was shot in the back and he was unarmed. What circumstances would have justified that?
You ignored the point that two of the officers (apparently) were not present for that shooting. So two of them, according to the articles, may have had nothing to do with the “in the back” shooting. Yet they are treated as guilty parties.
As for “in the back” we have to know all the facts, such as how close was he when the officer fired, was he attacking the officer ala Michael Brown, etc. The perp might have ambushed the officer. There are plenty of ways to cause grievous bodily harm without a gun. He might have been fighting and twisting, we don’t know anything yet. You don’t know that the officer knew he had no weapon. He might have been trying to get the officer’s weapon, or he might have done something threatening. I’m not going to try to list all the possibilities, I’m going to wait for a full presentation of the facts. If you care to make up your mind based upon the briefest of newspaper articles that is your concern.