Paul was a police officer for 30 years specialising in murder investigations both as a front line detective and senior investigating officer. He was seconded to the FBI in Quantico, Virginia in 1997 where he worked with a wide range of police officers and studied behavioural science. His other specialisms in the police were firearms command and football command. He retired with the rank of chief superintendent. Since 2014 he has been researching murder investigations in the early part of the twentieth century. He has published two books; The Long Silence (History Press 2021) and The Murder That Defeated Whitechapel's Sherlock Holmes (Pen and Sword 2018).