While I think we all have some sense of "I think he did it", it's not his job to file the court case and prove it for the family. The family made the accusation - it's THEIR job to prove that he is guilty of the charges.
I think you're speaking out of frustration for something that you "just KNOW happened", but put the shoe on YOUR foot. What if you were the one being accused of these things? Now, you're prolly saying to yourself right now "I'd never be found guilty, because I'd never do something like that". That's not the point in this case (or your case, since I asked you to put yourself in his shoes). The point is that you'd have to raise doubt that the accusations put forth are at least SOMEWHAT in doubt. That's all Mike's lawyers did - the exact same thing you'd be having to do in this situation.
The difference is that you feel it's glaringly obvious that he all but admitted that he did it, which ISN'T what this case is about.
Oh, and for the record, OJ was given credibel tips long ago that the real killer is an avid golfer in his area. His idea is to tell everyone he meets on the links that he forgot his golf glove at home and could he borrow theirs. When he finds the bloody golf glove, he'll spring into action, closing this case and clearing his good name.