An investigation into the case of doorman and car clamper Levi Bellfield, who committed three murders - including that of schoolgirl Milly Dowler in 2002. But would he have gone on to claim even more victims had he not made a string of mistakes that alerted police? Interviews with detectives, including the officer who interrogated Bellfield, as well as a former partner of the murderer, reveal the errors that led to his arrest