One aspect of the case that puzzled investigators was the fact that all six victims appeared to have died in their sleep, without struggle, and neighbors didn’t hear any gunshots, despite the fact that the rifle DeFeo used didn’t have a silencer. When DeFeo’s trial began in October 1975, his attorney argued for an insanity defense; however, that November, he was found guilty of six counts of second-degree murder and later sentenced to six consecutive sentences of 25 years to life in prison. DeFeo, who gave conflicting accounts of his story over the years, later claimed his sister Dawn and two other accomplices were involved in the murders.

The DeFeo house was sold to George Lutz, who moved in with his wife and three children in December 1975. The new owners resided in the house for 28 days, before they fled, claiming it was haunted by the spirits of the DeFeo family. Critics accused George Lutz of concocting the story to make money, but he maintained he was telling the truth. In 1977, Jay Anson published a novel titled The Amityville Horror. The book became a best-seller and inspired a 1979 movie of the same name, as well as a 2005 remake.