.
Who knew about Fredo's betrayal? Well, how did Tom find out? I'm sure Michael didn't tell him. Besides, why did Tom think that Fredo was in NY? Why would he know about Fredo's whereabouts in the first place? Or, if he did know, why would he only think he was in NY? Why wouldn't he know for sure if he knew at all?
I tried to address all those questions here:
http://www.gangsterbb.net/threads/ubbthr...true#Post472494