Arthur S. Turberville 
Medieval Heresy and the Inquisition 
How the Vatican Got Away with the Murders of Millions of Innocent People

Arthur S. Turberville details the Vatican’s doctrine underlying the violent Roman Inquisition, which was used to suppress all opponents to the Roman Catholic Church’s well-established religion. This book is not a detailed history of the Inquisition, but rather an excellent survey of literature on the Church’s doctrines on this practice.