I dunno, it would not surprise me to learn that they didn't have sex. Those pix of Arias on the bed (yucky!) could have been taken by her using the camera on auto timer.
This could have been done while he was doing something else in another part of his house. It was his camera, after all, the camera he was going to take on his Cancun trip the very next day (correction: in a few days, thanks for reminding me, Linda!) . What a shock it would be to him, not knowing those pix of her were on there, and then to find them later, perhaps while in the company of his friend, Mimi. I suspect this is what Arias was going for. But I could be wrong here. MOO.