I don't know if I completely agree with the fact that Fredo was in on killing Michael the WHOLE WAY. Although I find myself leaning that way, I think about the incident when Ola calls Fredo at his house late at night when Fredo's wife asks "who was that hunny?..."wrong number." In that phone conversation Fredo says "you guys lied to me." What did they lie about? Did they lie about the fact that they would guarantee Michael's death at Lake Tahoe? The fact that Ola and Roth 'lied' to Fredo reveals that Fredo no longer trusts Ola and Roth and no longer wants any part in killing Mike because he believes that they CAN'T KILL MIKE. Also, doesn't the fact that Fredo says "I don't want you guys calling me anymore" imply that he doesn't want to kill Michael anymore. I think this is one way that people could argue that Fredo WASN'T GOING ALL THE WAY in killing Michael.