<sod>Aspects of the novel were inspired by an [[Exorcism of Roland Doe|exorcism performed on a young boy]] from [[Cottage City, Maryland]], in 1949 by the Jesuit priest, Fr. [[William S. Bowdern]], who formerly taught at both [[St. Louis University]] and [[St. Louis University High School]]. Hunkeler's Catholic family was convinced the child's aggressive behavior was attributable to demonic possession, and called upon the services of Father [[Walter Halloran]] to perform the rite of exorcism.<ref>[http://www.strangemag.com/exorcistpage1.html] Strangemag</ref> Although Friedkin admits he is very reluctant to speak about the factual aspects of the film, he made the film with the intention of immortalizing the events that took place in St. Louis, Missouri in 1949, and despite the relatively minor changes that were made, the film depicts everything that could be verified by those involved. It was one of three exorcisms to have been sanctioned by the Catholic Church in the United States at that time. In order to make the film, Friedkin was allowed access to the diaries of the priests involved, as well as the doctors and nurses; he also discussed the events with the boy's aunt in great detail. Friedkin doesn't believe that the "head-spinning" actually occurred, but this has been disputed. Friedkin is not a Christian of any denomination.<ref>[http://thedianerehmshow.org/shows/2013-04-29/william-friedkin-friedkin-connection-memoir/transcript] The Diane Rehm Show</ref><eod>
<sod>Aspects of Blatty's fictional novel were inspired by the [[Exorcism of Roland Doe|exorcism performed on Roland Doe]] a young boy from [[Cottage City, Maryland]], in 1949 by the Jesuit priest, Fr. [[William S. Bowdern]], who formerly taught at both [[St. Louis University]] and [[St. Louis University High School]]. Hunkeler's Catholic family was convinced the child's aggressive behavior was attributable to demonic possession, and called upon the services of Father [[Walter Halloran]] to perform the rite of exorcism. It was one of three exorcisms to have been sanctioned by the Catholic Church in the United States at that time. Later analysis by [[paranormal]] [[Skepticism|skeptic]]s of the original 'Roland Doe' (or 'Robbie Mannheim') case have contended that Doe was likely a [[Mental illness|mentally ill]] teenager acting out, as the actual events likely to have occurred (such as words being carved on skin) were such that they could have been faked by Doe himself.<ref name=strangemag>{{cite web|url=http://www.strangemag.com/exorcistpage1.html|title=The Cold Hard Facts Behind the Story that Inspired "The Exorcist"|publisher=''Strange Magazine''|accessdate=August 10, 2015}}</ref> The novel changed several details of the case, such as changing the gender of the allegedly possessed victim from a boy into a girl and changing the alleged victim's age.<ref name=Susman/><ref name=strangemag/><eod>