In March 2011, a major police investigation was opened in the search for missing Swindon local, Sian O’Callaghan. When taxi driver Christopher Halliwell was arrested, Detective Superintendent Stephen Fulcher didn’t expect what happened next. After the body of another missing girl, Becky Godden-Edwards, was uncovered, the police had two murders on their hands and one suspect, but how many more unsolved murders could Christopher Halliwell be responsible for?