 Three years later, he published "The Riddle of Birdhurst Rise", a full-length study of the Croydon poison mystery of 1928.Both these books are recognized as classics in the field of true crime history, and after being reissued as Penguin paperbacks, they enjoyed considerable sales.In 1975, Whittington-Egan published a "Casebook on Jack the Ripper", which has been much sought after by collectors of Ripperine literature.