The Exorcist has terrified audiences since 1973, but few know the story is true. For the first time on television, investigators expose shocking secrets about the real-life exorcism of a 13-year-old boy that inspired an iconic horror film.

It began in the summer of 1980, when 11-year-old David Glatzel helped his older sister, Debbie, and her boyfriend, Arne Johnson, fix up the house they just rented.