I had a feeling that Rocco was a traitor too (although some very smart people here have posted counter-arguments that make me doubt myself ). I also think I'm one of the few people who believed that Rocco opened (or could have opened) the drapes. It looks like he's in charge of security on the grounds, so I wouldn't be surprised if he had access to the house.

When you made that post about the exchange of the orange, I thought that could be one more point in favour of the "Rocco as traitor" theory because it hints that Johnny Ola and Rocco know each other. I have to check my Godfather II tape for the scene where Johnny Ola arrives at Tahoe to see if there are any visual clues about this.