I know, I just mean that before BK left and before he ran into Xana she could have seen the slider open while in the kitchen and closed it, and then BK could have just opened it again to leave and left it open. I agree with your other post after the one I replied to that Xana might not have been immediately alarmed by the open slider and have just thought someone's boyfriend had come over. Especially because that particular night everyone in the house was out/up very late and at the time of the murders at least 3/6 of them were still awake (BF, DM, and Xana). Even the "someone's here" could have been more annoyed/curious than anything else- after all, DM didn't say anything about that particular line sounding distressed or anything.