Even Michael volunteers that 'Roth misled him' in order to beckon him home. That wasn't just to lull Fredo into a sense of false security. They all believed he knew very little, and provided just enough information (whatever that may have been - it's never revealed) to enable the plot to be carried out.
What did Michael think? Did he believe Fredo knew about the hit? When did he change his mind? During the boathouse conversation?
It's one of the moments that I don't really understand even though it's powerful: "Fredo you're nothing to me now you're not a brother, you're not a friend."
Was Michael angry because
- Fredo didn't deliver more infor about the hearing?
- Fredo by his epileptic behavior showed that he knew in fact it was going to be a hit?
- Fredo put his own interests over the family?
