Or, PF asked someone to kill her (someone who he thought shared his motive), he refused, so PF did it all on his own, later providing details to person X. Either motivated by a reward or the fear of being implicated, he contacts authority and strikes a deal. He either has possession of, or knows where the phone is, he has information on the general vicinity of where she may be, and he knows where she was killed (prompting LE to search her home a second time, gather additional evidence, and make the arrest)