 Humble's preoccupation with the Whitechapel murders influenced the writing of the hoax letters, some passages being paraphrased from the 19th century letters of the earlier serial killer.However, before Sutcliffe was arrested, Humble twice phoned the police anonymously to indicate they had been hoaxed because he felt guilty for misleading the investigation, but they were discounted.One call to Sunderland police on 14 September 1979, was 12 days after Barbara Leach was killed, the first of Sutcliffe's victims to be murdered after Humble's hoax influenced the police investigation.