In the dramatic scene when Michael exclaims, "Pentangeli is alive!", Tom concludes, "Roth played this one beautifully."

How did Tom know Roth was behind the perjury trap? Based on that scene alone, I'd have thought that the trap was laid by the FBI acting in concert with the Senate subcommittee chairman. They had ample motivation to trap Michael. It isn't until later, when Michael is alone with Fredo, that Fredo tells him, "The Senate lawyer, Questadt, belongs to Roth." I don't think Michael knew that until then.

Your thoughts?