Godfather 2 questions part 1?

Michael didn't know exactly who tried to kill him so he told all of the suspects he knew it was the other guy as part of his investigation to find out, to see their reactions. Michael never knew the truth until they were in Havana and he heard Fredo say he knew Roth before. Fredo probably did pull back the curtains but the real betrayal was that Roth must have told him he could be boss after Michael was killed and Fredo accepted that offer. I don't know who killed the would be ins but part of what makes the Godfather so great is what you don't see and have to think about. Roth just wanted the Corleone family eliminated so he could consolidate the power he already had over all the other families.