From TheMilwaukeeChannel.com - News - Priest Who Helped Inspire 'The Exorcist' Dies:
"A priest who participated in the 1949 exorcism that inspired 'The Exorcist' book and movie has died at age 83.
A funeral mass will be held Friday in a Milwaukee suburb for the Rev. Walter Halloran.
He was the last living Jesuit who assisted in the exorcism at a St. Louis hospital. Halloran died Tuesday night at a Jesuit retirement home in suburban Milwaukee.
Halloran was a 27-year-old Jesuit student when a priest called him to the psychiatric wing at a St. Louis hospital to help control a 14-year-old boy who he believed was possessed by a demon.
A brief news account of the incident inspired William Peter Blatty to write his 1971 best seller, 'The Exorcist,' which led to the movie a few years later."