A former girlfriend of mine was from Amityville, and lived down the street from the infamous dwelling. The story, as she told it, was that the "haunting" angle was concocted by the killer's attorney to buttress his insanity defense.

According to her, the kid who slaughtered his family had been terrorizing the neighborhood for years prior to the crime. Her most vivid memory of him was the night he jumped the fence of her house and eviscerated the rabbits she kept in a hutch out back (in keeping with the longstanding tradition of serial killers, most of whom inaugurate their careers by torturing animals to death). After graduating to murder, he claimed (IIRC) that the house was haunted by evil spirits which ordered him to kill, the idea being to establish that he was psychotic or schizophrenic. I don't believe this approach persuaded the jury, but the idea of a demonic suburban split-level was apparently convincing enough to lure legions of bored consumers to that squeaky wire rack of paperbacks in the corner of Walgreens.