That's horrible, what a load of monsters they must have been.
Just in regards to the screaming, I was wondering if he might have passed out from the booze/cocaine and not been screaming? Not that I think anyone in the house didn't know what was going on, I don't think you can keep such a huge event quiet from someone who is sitting down the corridor.
Homophobia plays a part in a lot of how Stuart's murder was perceived by the media and possibly also the people there. Maybe the women were sitting in the kitchen and heard loads of screaming, but the killers were maybe laughing and going "wahey" or whatever, so the women just rolled their eyes and ignored it, because "Ew, gay guys having an orgy, I don't want to know what that screaming is."
I don't know enough about cocaine or other drugs to know how it might have affected their reactions on the night. Is there any chance that they knew what was happening but found it funny or just didn't think it was urgent, because they were coked up? Then when they came down, reality sank in?