Interesting. Perhaps the locks were changed because it was a party house, and the girls didn't want people going into their rooms and taking their stuff?There are photos on social media of the girls in the house and you can zoom in and see 2 different doors that have number locks on the interior of the home.
However, it raises the question of how the killer accessed the rooms. Did they have the code, or were the locks disabled/doors slightly propped open? Personally, I can't imagine leaving the locks on all the time and having to punch a code in in the middle of the night when you come back from the bathroom.