I think some of you are going off track a little with regards to his behaviour.
Here's my train of thought...
His own mother seems to suspect he may have been moonlighting as an unlicensed taxi diver - an offence.
The side street he was parked up in is one of the few spots in that part of Beverley Road you'd be able to pull into. He was smoking a *advertiser censored* and hoping for some passing custom from the pubgoers. Haworth Arms is literally just a few yards around the corner, and there are other pubs like Gardener's Arms in the vicinity too. A lot of students in particular would be looking for a taxi to get home to their student digs on a night out.
It's pretty much a dead cert to me that he was touting for business. He'd probably been sat there innocently enough until he saw or heard Libby crying on the bench just a few yards round the corner. He smoked his *advertiser censored* and went to investigate. It is probably her we see getting into the passenger side. He assists by opening the door and guiding them in, but they're clearly not unconscious. They slip in easily enough, with a bit of a bump, and you can see them bounce slightly as they hit the seat.
The question is how he convinced her to follow him to the car. Maybe he played the whole "See, that other guy who pulled over could've been a monster, you really can't stay here. Let me take you somewhere safe."
I am betting on it not being premeditated in any way prior to him spotting her. It was just opportunism. He was angling for business in a convenient place. He stumbled into her and could see she was in a pretty sorry state. Maybe he just planned on helping. Maybe not. Perhaps even at the point in the footage we see her getting into the car, he still had no ill intent. The question really seems to be what happened between the point of him picking her up and her going missing. Did she have second thoughts? Did he try it on? Did she? Did he say something that creeped her out? Where did he take her? Why? Is that the point at which she realised something was wrong? Did they return to her address or head straight somewhere else?
Based on the CCTV footage here it's pretty clear to me the series of events that led up to her being picked up. It's what comes afterwards that remains a total mystery.
