So if he suspected Fredo just a little bit, why didnt he latch upon what Fredo said at the cafe

Fredo - I was mad at you....
Mike - What? What do you mean?
Fredo - Oh nothing
Mike - Come on Fredo, what
Fredo - Well...when I said I didnt know Ola, I wasnt being honest, because I'm scared of what will happen when you find out
Mike - Found out what
Fredo - I told Ola things about you I shouldn't have, I'm so sorry Mikey, its my fault you got hit, but I SWEAR I didnt know it was going to be a hit.

I dunno, something like that. Mike was so gone though, he would have killed Freddie even if he confessed in the fashion seen above