Watched both last night, bloody hell.
The thing that jumped out at me was in the first interview with him, when he was telling them that she'd left with a mystery woman, was that he was clearly lying (you can tell after some time when people are making things up) so it was obviously fishy from the start! Maybe they didn't want to show any bias without the evidence but if I'd been in the room my Spidey senses would be tingling! (Not a cop, interview for other reasons).
The comparison to Ben Field is spot on and the DCI was totally right he must have previous for something similar.