Ronald Joseph DeFeo Jr. (September 26, 1951 – March 12, 2021) was an American mass murderer who was tried and convicted for the 1974 killings of his father, mother, two brothers, and two sisters in Amityville, New York.

One of the group, DeFeo's friend Joe Yeswit, made an emergency call to the Amityville Police Department, who searched the house and found that six members of the family were dead in their beds.

"[3] He admitted that he had taken a bath and redressed, and detailed where he had discarded crucial evidence such as blood-stained clothes, the Marlin rifle, and cartridges, before going to work as usual.

The psychiatrist for the prosecution, Dr. Harold Zolan, maintained that, although DeFeo was a user of heroin and LSD, he had anti-social personality disorder and was aware of his actions at the time of the crime.

[9] The trial's judge, Thomas Stark, declared that DeFeo's crimes were "the most heinous murders committed in Suffolk County since its founding.

[11] DeFeo was held at the Sullivan Correctional Facility in the town of Fallsburg, New York, until his death in 2021, with all of his appeals and requests to the parole board being denied.

In this interview, DeFeo also asserted he was married at the time of the murders to a woman named Geraldine Gates, with whom he was living in New Jersey, and that his mother phoned to ask him to return to Amityville to break up a fight between Dawn and their father.

Evidence was submitted to the court by the Suffolk County District Attorney's Office suggesting that Richard Romondoe did not exist and that Geraldine Gates was living in upstate New York married to someone else at the time of the murders.

Geraldine Gates did not testify at this hearing, because the authorities had already confronted her about the false claims; in 1992, they had secured a statement under oath in which she admitted that Romondoe was fictitious, and that she did not actually marry DeFeo until 1989 in anticipation of the filing of the 440 motion.

He produced no corroborating evidence in this regard... another reason for my disbelief of defendant's testimony is demonstrated by consideration of several portions of the trial testimony... he signed a lengthy written statement describing in detail his activities... in this statement he said that he lived with his family at 112 Ocean Avenue in Amityville and that he worked for his father... that he usually went to and from work with his father; that he was ill and stayed home from work on November 12, 1974; that he was on probation for having stolen an outboard engine and had an appointment to see his probation officer in Amityville on that very afternoon... defendant's girlfriend, Mindy Weiss, testified that she began dating the defendant in June 1974, and was with him frequently that summer and fall."

[19] According to Osuna, DeFeo claimed that he had committed the murders with his sister Dawn and two friends, Augie Degenero and Bobby Kelske, "out of desperation," because his parents had plotted to kill him.

Allegedly, DeFeo claimed that, after a furious row with his father, he and his sister planned to kill their parents and that Dawn murdered the children to eliminate them as witnesses.

Police found traces of unburned gunpowder on Dawn's nightgown, which DeFeo proponents allege proves she discharged a firearm.

Skeptic Joe Nickell noted in 2003 that, given the frequency with which DeFeo had changed his story over the years, any further claims from him regarding the events that took place on the night of the murders should be approached with caution.