This has been discussed before, but I’m raising it again, hoping we might have some new insights:

Michael didn’t initially suspect Fredo of complicity in the Tahoe shooting. When he told Tom, “Fredo? He’s got a good heart. But he’s weak and he’s stupid—and this is life and death,” he was saying that Fredo didn’t have what it took to run the family in his absence—not that he thought Fredo might be a traitor.

Some here think Michael might have had Fredo bring the $2 million to Havana in order to test him. I think Michael had sound tactical reasons: Tom was needed to run things in Nevada. And, by not using Rocco and/or Neri, Michael was signaling Roth that he still hadn’t ruled out one or both as traitor(s).

And yet: as most of us have remarked, Michael gives Fredo two suspicious, piercing looks: when Fredo asks if anyone he knows is in Havana (and Fredo denies knowing Ola and Roth); and at the nightclub, when Michael “introduces” Ola to Fredo, and Ola says, “we never met.” The close-ups on Michael’s face show Michael looking intently at Fredo’s response, as if trying to see if he was lying.

Also, Michael probably arranged for the plane to take him out of Havana as soon as he learned when and how Roth planned to have him killed. That was before he had his intimate chat with Fredo over drinks. But, he didn’t tell Fredo about the plane at that time--he waited until after he learned that Fredo was the traitor--possibly another sign of suspiciousness.

With that in mind: Why, if Michael had any suspicions of Fredo at all, did he let Fredo in on Roth’s plan to kill him—and his plan to kill Roth—even telling Fredo that “Hyman Roth will never see the New Year"? What’s more, Michael didn’t even need Fredo to do anything: when Fredo asks what he can do to help, Michael says, “You just go along.” What was he thinking? Why did he tell Fredo?