Wow..... this is a bit of a thorny issue, and not one I'd really given any consideration to until now.

But I've got too agree that Fredo didn't know. After Michael supposedly "forgave" him, his relief is palpable, I truly think he believed he was back in the fold.

When he runs away from Michael, that is out of panic and confusion, and not knowing who to trust....Michael, Roth......the whole nights events had shook him up.

I agree that Fredo does display a look of resignation when Anthony leaves to "go to Reno" instead of going fishing, but I think that is probably more disappointment on Fredo's part, he had obviously planned a fishing trip with his nephew and that had fallen through. He probably also hoped that getting closer to Anthony would bring him closer to Michael. Besides, Fredo often had that "oh well" expression. If Fredo had sussed what was going on at that stage, he would have bolted. He is basically a cowardly character and its not really in his nature to face his death like some kind of samurai warrier.