Apple you never cease to suprise me I can't believe you said all of that, your pathetic. Now back to the topic which is what we are here for.
For the reasons I believe Fredo knew it was going to be a hit. Who left the drapes open? I believe it was Fredo no one else inside the Family was ever implicated in the plot other than Fredo. I also think it is highly unlikely that the shooters themselves would come in and do so. Even I think apple can agree with that. However I won't be suprised if she doesn't.
Also I believe Fredo was mis-led by Roth but in a different way. I feel Roth mis-led him in believing what would happen after Michael was killed. I think Fredo was under the impression that he and Roth would be on the basis of say Roth and Vito in the old days. I back this up by Fredo trying to be like his father in the second one. Sporting the mustache that Vito had in GF I as well as saying to Michael in Cuba "For once be more like pop."
I think that the shooters themselves were given the grounds of the estate by Fredo himself. I think there was pre-arrainged meeting point that they were suppose to go. When they got there though they were murdered not escaping which was probably the plan.
Also i'm not sure I want to make that clear to apple esp. I'm not sure but my interpetation of the look given by Michael to Fredo after "I swear I didn't know it was gonna be a hit" was more like "do I look that stupid to you?" thats just my interpretation of it. Its not the truth and I don't claim it to be. I just think its interesting b/c it doesn't leave any holes. If you find one bring it up b/c I would like to hear it.