I know the fun of these boards is to engage in speculation about things we don't see on screen but at least the speculation is usually grounded in things we do.

We don't see who opens the drapes but some of the posters here have made the assumption that Fredo did and have built all kinds of theories on that nonfactual foundation. Many of the posts here, as Don Lucchesi would say, are built on mud.

You can't credibly argue that Fredo knew it was a hit or was promised the Donship or anything else if your primary piece of evidence is "Well, he opened the drapes." Because you don't know that he did.

Pete has a very lucid post about an alternative theory (which I happen to agree with). He's been dismissed and shouted down.

I support the argument that it was likely one of the extra security men that was brought in to the party. It's certainly reasonable to think that security would have access to the bedrooms. Seems silly that they would be forbidden from inspecting the house prior to Michael's return.

Another point in favor of the traitor being a muscle guy is that it also provides an answer to the other big question from that scene: Who killed the assassins?

Unless we're going to say that the Fredo of GFII was not only "cunning and devious" but also an accomplished killer, there being a different inside man from Rocco's crew seems much more likely.