Over five years in the late 1970s, the Yorkshire Ripper was murdering women and the hunt for one of the UK’s worst serial killers was on. During this time, the police were sent three letters and an audio communication, purportedly from the killer – clues that led the investigation to be moved from West Yorkshire, where the Ripper (later to be named as Peter Sutcliffe) was indeed operating, to the north-east of England.