I've started to wonder if Claudia wasn't in a relationship with her killer, and instead he was a man who thought that she was 'easy' and that she definitely would be 'up for it'. Then she turned him down and he couldn't handle rejection from a woman who he perceived as very happy to sleep with all these other men, but not him.
In this scenario, he could easily be a neighbour or work colleague who Claudia would have trusted. Claudia would have been willing to accept a lift from him, not having a clue about his real intentions.