Sorry to say, I think there are a fair few Wayne Couzenses out there, although fortunately not bouncing around with a warrant card (one hopes). If Leah was abducted and murdered, it's far more likely to have been someone else entirely, not him imo.
As a side-note, when I first saw a police warrant card, I was extremely unimpressed and couldn't believe it was the real thing. I would guess most people haven't seen one, so I'm a bit sceptical of the idea that someone would be much more compliant when confronted with a real one belonging to a real police officer. I think just announcing that you were a plain clothes officer and flashing something vaguely similar could easily have the same effect on a well chosen victim, so imo WC himself is an unnecessary (and quite implausible) addition to this hypothesis.
And as a side-side-note, my father - who in fairness had dementia at the time - once gained access to a crime scene by flashing a Tesco Clubcard at a uniformed officer, who definitely should have known what a warrant card looked like. So the symbolic power of the words "I'm a police officer" definitely can't be underestimated.
Over all, I don't warm to this theory though, if I'm honest.
