Wow, a lot of new info just in the one brief piece! One thing that struck me was that I have always thought BK only wanted to kill. After hearing of those searches on his phone, I am now wondering if perhaps he did have other plans for Maddie, before killing her, and Kaylee's presence thwarted those plans, and may have provoked rage from BK, possibly contributing to what seems to be a more vicious attack of Kaylee.
ETA: The more I think about it, the less likely I am to believe that he would have done anything that knowingly could have left his DNA behind, so maybe that was just sick fantasy, and he got off on looking at sleeping or otherwise vulnerable women, knowing that he COULD have his way with them. JMO