Arne was a real person and as in the movie, he was dating, and later married Debbie Glatzel, David’s sister. During one of David’s exorcisms Johnson supposedly challenged one of the many demons supposedly possessing David and invited the demon to leave David and possess him instead. Following this incident Johnson apparently began to display odd behaviour similar to David’s.
As in the movie, Debbie worked at a dog kennel and her employer was also her landlord. Unlike in the movie, where he’s called Bruce (played by Ronnie Gene Blevins) in real life his name was Alan Bono. On the day the murder was committed Arne and Debbie were with Arne’s sister Wanda and Debbie’s 9-year-old cousin Mary. They had been out for lunch with Bono who had been drinking. Later on an altercation took place where Bono grabbed Mary and Arne ordered him to release her. Debbie apparently tried to de-escalate the situation but Arne started growling like an animal then pulled out a knife and stabbed Bono to death. As in the movie, Debbie was a witness.
The Disciples of the Ram
The Disciples of the Ram aren’t real but they might be loosely inspired by real cults such as the Manson family – this lot appeared first in the movie Annabelle which is a fictionalised back story of the doll (which is a real doll which was kept in the Warren’s artefact room).
Katie and Jessica
The murder of Katie by Jessica and Jessica’s apparent suicide straight after aren’t real and the film doesn’t give a massive amount of backstory about these two. However, DC Comics has launched a new book titled DC Horror Presents: The Conjuring: The Lover #1 which specifically focuses on Jessica and how her possession comes about – it works as a direct prequel to the movie.
Kastner and the occultist
Certainly no mention of these elements of The Conjuring:The Devil Made Me Do It were ever brought up in the real case. These parts of the film lean into the Satanic Panic of the 1980s implying that David Glatzel was deliberately cursed by a devil worshipper looking to gain great power. It’s a fun bit of horror which nods to other genre films and allows the Warrens to have an adventure with an actual antagonist rather than making the film a courtroom drama.
The court case
It is true that Johnson’s lawyer – a man named Martin Minnella – did try to present possession as a defence but the judge wouldn’t permit it. Instead Arne’s lawyers went for a self defence plea. He got convicted of first degree man-slaughter, was sentenced to 10-20 years in prison and served five.