...but I think Michaels suspicion arose when the shooting took place in the middle of his own compound right in his bedroom. The enemy had to be an insider to easely squeeze through those gates and make his way straight to his home.
Of course he knew that only an insider could have gotten that close to killing him (and Kay). The issue was: who? Roth would have him believe that Pentangeli was behind it, but Michael saw through that ruse. In doing so, he saw that someone "
very close to us [emphasis added]" was involved..."very scary." Yes it was!
Its a common lesson taught to us in the Godfather series that your worst enemy is always close to you, he's an old friend or a family member, even Michael knew so since he warned Vincent in GF3 about that. (How he had to chose between the life or Mary, because when his enemies would come they'd come after her or everything close to him, and they'd be close to him too)
he found out that Altobello was behind the Atlantic City attack, and
after learning that Sicily's top assassin--a man who never misses--is gunning for him, what does Michael do? He gathers his family around him inside and outside of a crowded public venue, making all of them sitting ducks for that assassin. It was Michael at his most arrogant and irresponsible.
