Some of the aspects of this case remind me of Dani Stickliski (sorry for the misspelling) who went missing after her coworker disappeared her. It was unclear whether they were having a relationship or he was just an obsessed creep who created a ruse to get her to follow him to his house, or something like that.
It IS possible that Carolyn was "drawn home" by an unrelated issue, mentioned it to this guy, and he saw it as his opportunity to isolate her and kill her, for whatever sick twisted motive he had, perhaps slipping in behind her as she went into her apartment (although neighbors say she was alone). On the other hand, it does seem easier and more logical that it was a planned meeting from a logistical standpoint but more puzzling if she did have a relationship with him. If that was the case, hopefully LE knows the timing. Did she leave first from the office, he followed immediately or a little after? The timing would be really critical.
He does perhaps sound like an injustice collector - the keying of cars, the lying, maybe he was also a narcissist sociopath.