A fellow named Kajieme Powell was shot dead by police in St. Louis on August 20th. This case is not as egregious as what we know about the Michael Brown incident. It just speaks, at the very least, to the lack of professionalism in St. Louis law enforcement. Powell was not in his right mind and had a steak knife. It seems to me that police are sufficiently well-paid that two of them could have taken a chance on arresting Powell without killing him. As explained here, the initial police error that made the ensuing tragedy nearly inevitable was their failure to stop and get out of their cruiser a sufficient distance away, rather than put one of their own in immediate danger.
By contrast, see below the video of a confrontation in London between unarmed police and a black man swinging a machete. (It is not obvious from the video that Powell was set to use his knife, though he was advancing on one policeman.) The London police are patient enough to eliminate the threat without violence.