And if anything, after Fredo's outburst in that boat house scene, Mike should have realized even more that Fredo didn't realize that there was going to be a hit.
Michael knew all that when he talked to Tom in the boathouse right after the failed hit.
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
