But there's only one way Fredo could have known that the Senate lawyer, Questadt, belonged to Roth: Roth told him. And, if Roth told him, it tells me he was in with Roth far deeper than he let on.
While this is a logical chain of inference its foundation makes no sense.
As Oli points out, there was no reason to give Fredo such inside details on Roth's plan. Fredo was hardly a vault with information, and he had already told Ola that he didn't want to talk to them anymore after the failed hit. The phone conversation also confirms to me (but, admittedly, not to everyone) that Fredo didn't know it was a hit and he felt deceived by Roth. Nothing here lays the groundwork for continued confidences from Roth to Fredo.
Also, Fredo had no value to Roth after the Tahoe hit attempt. Why would Roth need Fredo's complicitly to kill Michael in Cuba or to have Michael perjure himself? Keeping Fredo in the dark would have been much safer.
The only reasonable explanation I can see is that, during his interactions with Roth, Fredo somehow came across Questadt. Then, after seeing him at the Hearings, Fredo put two and two together. While that information would have been useful to Michael, it does not mean that Fredo was in deeper with Roth than previously acknowledged and certainly doesn't mean that Fredo knew about Pentangeli and the perjury trap.
