Everyone please keep in mind Fredo's attitude when Michael found out about his treachery. Fredo wasn't the least bit contrite. Instead he went off on a rant about how he was passed over, how he had to run mickey mouse night clubs and take people to the airport. So even after the attempted hit, and with the knowledge Micael was facing a perjury rap, Fredo was still angry and resentful. IMHO the only reason he gave
Michael the information that they had Pentangeli (which Michael already knew) and that Roth owned Questadt was a lame attempt to keep Michael from killing him.