While The Amityville Horror films focus on the hauntings and dark spirits that exist in the house, what caused those paranormal symptoms was the mass murders that Ronald Joseph DeFeo Jr. committed against his family inside the house on November 13, 1974. At the time, DeFeo Jr. was just 23 years old.

Yes. Although the names have been changed, the story is based on the 1974 murders of the DeFeo family in Amityville, Long Island, New York.