“The Nativity with Sts. Francis and Lawrence” plays an important role in my new Caravaggio novel “A Name in Blood.” In 1969, it was stolen from the Oratory in Palermo, Sicily, where it had been displayed for 350 years. Naturally the Mafia was suspected. Various mafiosi have offered explanations for what happened. The Christian Science Monitor reports on a new book about the theft, theories of where the masterwork might be, and the manipulation of Italian authorities by mafiosi claiming knowledge of its whereabouts.