I reckon that was just psychopath banter from Cannan. He's living the rest of his days in prison, on prison food, wearing prison pants, having one shower a week and a prison haircut once a month. How else can he kid himself he's a winner, one wonders, other than by twitting the police and getting them to dig up random places? What larks! If he were a Spurs supporter, he'd no doubt have told the plod - or some stool pigeon - that she is buried under Arsenal's pitch. And then sat back to watch the fun as the bill dug their pitch up.
Being a card-carrying psycho, he could easily have done that regardless of whether he knew anything about the case or not. One thinks of the Ripper tape hoaxer, who disliked the police and knew just enough about the case to hoax them and make them look foolish. It gave him 25 years of laughs too, until they DNA tested the envelope he'd licked.