It says a lot about the American police system and the level of protection they give themselves, that even in this situation I think the only reason they got done so quickly was because they couldn't control the CCTV video. That part is just clear murder, which can not be hidden. The man is defenceless and out of it, yet is still kicked in the head and held up to be hit. If it was just the blurry body cams of this part, I wouldn't have put it past them to just sweep it under the rug.
From how they talked about it after, and the total lack of reaction as other officers arrived and saw them/heard them talking about it, it is clearly something that this police department has done before. Whether the previous victims survived or the evidence wasn't there unlike this case, its clear that the behaviour is normal for them.