An interesting discussion in the “When did Michael decide to kill Fredo” thread has made me believe that Fredo was in with Roth and Ola far more deeply than I’d previously thought:

Probably no more than 48 hours elapsed between Michael’s departure from Cuba and his meeting with Tom, Neri and Rocco in Nevada—Michael’s wearing the same clothes as in Cuba, looks exhausted, asks Neri for a wet towel…As soon as he’s alone with Tom, he asks:

Where's my brother?
TOM: Uh – Roth got out on a private boat, he's in a hospital in Miami. Had a stroke but he recovered okay. Your bodyguard's dead.
MICHAEL: I asked about Fredo.
TOM: Uh -- I think he got out -- he must be somewhere in New York.

--Tom had been in Nevada all the while Michael was in Cuba. How could he have known that Roth had a stroke, had recovered, got out on a private boat, and that Michael’s bodyguard was dead? Roth sure didn’t tell him.

--The last we saw of Roth, he was gravely ill, unconscious, breathing on oxygen—and nearly dead from the bodyguard’s attempt to asphyxiate him. How did Roth get on that private boat so quickly? Not under his own power, surely.

--The last we saw of Fredo, he seemingly was running from Michael, dazed, nearly hit by a car. Michael’d had the foresight to arrange a private plane out of Cuba, but Fredo wasn’t on it. How did dumb, simpleminded Fredo get to New York in that same 48-hour-or-less timeframe?

What this suggests to me is:

1. Fredo told Tom about Roth’s stroke, escape, and the bodyguard.

2. Roth had either arranged the private boat for himself ahead of time, or someone rescued him. It may have been his pals in the Cuban government. Or, it may have been Fredo, via his own contacts in the Cuban government. Either way, Fredo had to have been on that boat with him—that’s how he knew about Roth’s escape and the bodyguard’s death.

3. Since Fredo was included in Roth’s escape plan, he had to have been far more important to Roth than simply as a dupe for the attempted Tahoe massacre.

Put this together with other hints: “Johnny Ola brought me here [to the Superman show] implies that Fredo’d been to Cuba with Ola before. “I’m gonna get me a real drink” may have been Fredo leaving the Presidential Palace to phone his contacts in the Cuban government because the next thing we see is that smart-looking military detachment double-timing down the hospital corridor to rescue Roth. And, in the later boathouse scene, Fredo knows that Pentangeli survived, and that the Senate lawyer, Questadt, belongs to Roth.

All of this suggests that Fredo not only an active part of the plot to murder Michael in Tahoe, he also didn’t expect Michael to get out of Havana alive—and may have tried to prevent Michael’s escape. And, even after Michael got out, he and Roth still may have been conspiring against Michael. Part of that conspiracy may have been Fredo’s failure to tell Michael about Pentangeli and Questadt, when doing so before Michael’s Senate testimony might have gotten him back in Michael’s good graces.

Small wonder Michael killed his own brother.