Well, it is true that Rudy himself went out dancing at Domus purposely to create an alibi for himself - but what good does that do, for him, or Amanda and Raffaelle, by causing a disturbance, if it is after the time of the murder? We know it did Rudy no good.
As for the unlatched door--- it still could point to someone in the cottage, which because the other girls were away, leaves only Amanda , and Rudy as an annex to "the boys downstairs". A break in with smashed window is supposed to scream, "outsider, stranger".