The latest horror film, The Conjuring: The Devil Made Me Do It, purports to be based on a true story. Of course, many horror films have claimed to be based on true events in the past, ranging from The Blair Witch Project (which pretended to be a true documentary) to The Texas Chainsaw Massacre, which was inspired by the crimes of Ed Gein, who never committed a massacre, never used a chainsaw, and was not from Texas. Similarly, the third film in the Conjuring series (and the eighth overall) is based on a true tale, but the fact of what happened in the case of Arne Johnson (Ruairi O’Connor) differs from what transpired in The Devil Made Me Do It in a number of crucial ways.
Members of the Glatzel family have claimed in movies about these occurrences that David began having visions of a strange guy after they moved into a new residence. He started suffering night terrors and woke up with mysterious scratches and bruises soon after. They had a Catholic priest bless the house, and the Warrens came 12 days later. The couple later claimed that he levitated, foresaw the murder Johnson would do, and was choked by invisible hands during the exorcisms they performed on him (a video from one of which plays at the end of the film). Of course, how much of this you believe depends on whether you believe the Warrens were really demonologists (as Th. claims). IMDB