Who Killed Emma?

Emma Caldwell was a young woman from a good home who developed an addiction to heroin after the death of her sister and then descended into street prostitution. When her body was found dumped in a ditch in Lanarkshire in May 2005, the police launched an unprecedented murder hunt. But ten years on, after an investigation costing millions of pounds, no one has ever been convicted of her killing. Eamon O Connor investigates what went wrong. Producer: Ian Muir-Cochrane.