Michael Jacob and Daniela De Gregorio write together as Michael Gregorio. Daniela teaches philosophy; Michael is interested in the history of photography. They live in Spoleto, a small town in central Italy. They have created a series of crime novels whose central charater is the Prussian magistrate, Hanno Stiffeniis. The series includes Critique of Criminal Reason, Days of Atonement, A Visible Darkness and Unholy Awakening.