Code of a Killer is based on the extraordinary true story of Alec Jeffreys’ discovery of DNA fingerprinting and its first use by DCS David Baker in catching a double murderer. Code of a Killer focuses on how Jeffreys’ science (played by John Simm) and Baker’s (David Threlfall) investigative vision created the single biggest leap in the history of criminal investigation. Made by Line of Duty producers World Productions, Code of a Killer has been written by Michael Crompton (Kidnap & Ransom) with the full knowledge and input of retired Professor Sir Alec Jeffreys and former Detective Chief Superintendent David Baker.