I've seen an interesting television program about this case. From the article at the above link, under "Literature and Film":
"This exorcism case inspired the 1971 novel The Exorcist by William Peter Blatty, which in turn was adapted into the classic 1973 horror film of the same name. The case also inspired the 2000 movie Possessed, which is said to be closer to the story in Allen's book. A documentary was also made of the case, titled In the Grip of Evil. Another documentary movie was made in 2010 named "The Haunted Boy: The Secret Diary of the Exorcist" where a group of investigators travels to the location in question and uncovers the diary that is said to be kept by William S. Bowdern."
I just read your link-I thought the boy lived in Georgetown DC?
__________________ "Is all that we see or seem
but a dream within a dream?"
-Edgar Allan Poe
"...the man and the peaked cap he is said to have worn
quite tallies with the descriptions I got of him."
-Frederick G. Abberline