One thing that's always puzzled me:

Michael was frantic to get Fredo on that plane out of Havana--I'm guessing because he wanted to pump Fredo for more information on his betrayal. First thing he asks Tom when he's back in Nevada is, "Where's my brother?" But when Tom tells him that he think's Fredo's in NY, Michael simply says, "Get word to him," etc. Suddenly the pressure was off. Michael could have arranged to have Fredo found and brought to him ASAP. Instead, he waited until after his ass got into a crack at the Senate hearing befoe telling Tom, "I want to speak to Fredo."