To quote from Snopes:
The truth behind The Amityville Horror was finally revealed when Butch DeFeo’s lawyer, William Weber, admitted that he, along with the Lutzes, “created this horror story over many bottles of wine.” The house was never really haunted; the horrific experiences they had claimed were simply made up. Jay Anson further embellished the tale for his book, and by the time the film’s screenwriters had adapted it, any grains of truth that might have been there were long gone.
