West Country Christopher Halliwell

Sian O'Callaghan, from Swindon, disappeared after getting into Christopher Halliwell's car on 19 March, 2011.

The Confession, tells the story of how Det Supt Steve Fulcher - played by Martin Freeman - breached protocols to catch a killer.

The former police officer who, at one stage, led the Christopher Halliwell murder investigation has written a book about the case.