Sorry but I really don't believe that Fredo opened the drapes. Sure, he wanted to "handle things", but I seriously don't believe that he would do that. I'd like to believe that when Johnny Ola came on board, some of his men sneaked in and opened the drapes way before the party ended. Also, hasn't anyone consider that maybe Fredo's men could have killed Roth's assasins-to-be? You see, they could approach Fredo after the hit, Fredo is scared the living hell of it and orders his men to kill them, without leaving a trace. Remember, when Michael gave control to Tom, he mentioned that he would have power over all, and among other people, "Fredo and his men". I think thats what happened. Fredo's stupidity left him dead in the end of all.