Since they were neighbors, he would also have been parked on the fifth floor.
If he removed her from the building, I find it a lot more plausible that he grabbed her in the garage and then left the premises, probably immediately. (Which may have been what led law enforcement to investigate him more closely, because his vehicle would then have been on camera. It's also possible that it was an atypical time for him to leave, so it stood out )
However, if he'd gotten her into his apartment, it's likely she was recovered from there because of the difficulty of leaving without being noticed. (Unless of course he did try the large suitcase or other container stunt... which I'd imagine would have gotten attention, too )