When Rainer Decker was researching a sensational seventeenth-century German witchcraft trial, he discovered, much to his surprise, that in this case the papacy functioned as a force of skepticism and restraint. His curiosity piqued, he tried unsuccessfully to gain access to a secret Vatican archive housing the records of the Roman Inquisition that had been sealed to outsiders from its sixteenth-century beginnings. In 1996 Decker was one of the...