The only thing I know for sure is that my impression that he was an English Bulldog was wrong based on the video but it is unclear beyond that.
If this dog is really a "Pitbull", the Saturday Night Special Pitbull you can buy at the fairgrounds flea market for $100.00, than I would be more inclined to justify self-defense on the part of the shooting officer. That dog in the video was indeed agressively coming after the cop. Whether it planned to bite him or beat him to death with his tail can not be determined from the video. A lot of pitbull owners are coming up with different names and ways to describe their dogs because of the negative image of the name "pitbull". Show me a clear photo of the dog, that's all.