I'm confused as to why some ppl are still in doubt as to the extent of Fredo's guilt -- Fredo was in with Roth the WHOLE way.

FFC gives us definitive evidence of this in the penultimate boathouse scene when Fredo divulges his knowledge about Pentangeli being in Gov't custody and Questadt belonging to Roth. B/c of course, the only way Fredo could have this info is if he was in the closest of contact with Roth for the duration of the film. Shortly after the botched Tahoe attempt, Fredo tells Ola via phone NOT to call him anymore, but we know that's not the way things shaped out. B/c Roth, of course, wouldn't have formed his Pentangeli/Questadt plan until quite some time after the botched Tahoe attempt (he expected to easily kill Mike in Havana anyway) so thus we can infer that Fredo was in contact with Roth/Ola the WHOLE way, baby.

Thus it makes good sense to assume that Fredo was still trying to help Roth remove his brother at the New Years Eve party in Havana. And now knowing the depth of Fredo's involvement, we can infer that Fredo was in fact on his way to tip the police off when he went to get his "real drink".

So, of course Roth helped Fredo escape. As Turbull has noted before, Fredo must have called Tom after Havana. The only way Tom could have knowledge of the bodyguard's death AND Roth's heart attack/escape by boat (a boat that Fredo is also on) would be if Fredo knew. And if Fredo knows, then we can naturally infer he is still cahoots with Roth and thus Roth got him out of Havana.