Well,he should not have not killed his own flesh and blood,no matter what the reasoning behind it.That was an ugly and terrible thing to do.I believe that Fredo really was in the dark about Roth wanting to kill Micheal. He was sweet and honest,(in his heart)and he would have never willingly participated in somthing like that.Like the time that Connie told Mike to forgive him beacuase he is "sweet and helpless without him". And when Fredo embraced Mike,that is true. Which is why I do not think Micheal believed that Fredo had anything to do with the shooting.