Yes, indeed--what did Fredo think he was opening the drapes for? If--repeat, if--Michael hadn't decided to kill Fredo at that point, his statement could have been taken as proof that Fredo did know it was gonna be a hit, and was lying to save his life.
On the drapes thing maybe Ola told Fredo that Mike would soften up on the negotiations if he had some sleep deprivation.
I recall that before Michael met with Fredo, he asked Tom what Fredo knew, and Tom said that Fredo tld him he didn't know anything. AT that point Michael says h wants to speak to him personally. In that conversation he learns that Fredo knew that Questadt belonged to Roth, this means Fredo had lied to Tom about what he knew of the Senate investigation, so really the "I didn't know it was going to be a hit" makes it two lies Fredo told in that scene.
This raises the question, that Fredo opened the drapes knowing full well it was going to be a hit, and perhaps he thought he would become the new head of the Corleone family after Michael was out of the way. This sort of dispels the whole "good heart" thing, which I've never fully bought anyway.
