Think objectiv and listen to his testimony (ies). He is honest and unbiased (my view)!
As you are, I am biased as fuck, too! Horowitz has proven a lot of shit in his reports and he said they should be prosecuted! He has not the ability to subpoena anyone and no one was talking to him until the very end! And he is not able to interview fired people. In my opinion, he has done a great job, exactly by the book!