I must respectfully disagree with you TB, and go along with Leslie on this one.

I take it at complete face value when Fredo tells Mike "I didn't know it was gonna be a hit". But even if you want to discount that statement because he had incentive to lie to Mike, his statements to Ola ("You guys lied to me...you got me in enough trouble already"), to whom he had no reason to lie, cannot be discounted.

The more important question for me, as many of you know, is "Who killed the assasins?"

Again, taking certain character's statements at face value is one device a screenwriter uses to move the plot along. When Mike says to Tom something like (not the exact quote, here) "Unless I'm mistaken, they're dead already...killed by someone close, inside, afraid because they (the killers) botched it", I believe we are meant to think Michael is 100% correct in his analysis. And since, IMO, it is ridiculous to think that Fredo killed them, there is the inference of traitorous conduct by someone other than Fredo.