At around 6:30 PM on Wednesday, November 13, 1974, 23-year-old Ronald DeFeo, Jr. burst into Henry's Bar in Amityville, Long Island, New York and declared: "You got to help me! I think my mother and father are shot!" DeFeo and a small group of people went to 112 Ocean Avenue, which was located not far from the bar, and found that DeFeo's parents were indeed dead. One of the group, Joe Yeswit, made an emergency call to the Suffolk County Police, who searched the house and found that six members of the same family were dead in their beds.

The victims were car dealer Ronald DeFeo, Sr. , Louise DeFeo, and four of their children: Dawn; Allison; Marc; and John Matthew. All of the victims had been shot with a .35 caliber lever action Marlin 336C rifle at around three o'clock in the morning of that day. DeFeo's parents had both been shot twice, while the children had all been killed with single shots. Louise DeFeo and her daughter Allison were reportedly the only victims who were awakened by the gunfire at the time of their deaths, and according to Suffolk County Police the victims were all found lying on their stomachs in bed. The DeFeo family had occupied 112 Ocean Avenue since purchasing it in 1965. The murdered members of the DeFeo family are buried in nearby Saint Charles Cemetery in Farmingdale.

Ronald DeFeo, Jr. was the eldest son of the family, and was also known as "Butch". He was taken to the local police station for his own protection after suggesting to police officers at the scene of the crime that the killings had been carried out by a mob hit man named Tony Mazzeo. However, an interview with DeFeo at the station soon exposed serious inconsistencies in his version of events, the following day he confessed to carrying out the killings himself and Mazzeo had an airtight alibi proving he was out of state at the time of the killings. DeFeo told detectives: "Once I started, I just couldn’t stop. It went so fast." He admitted that he had taken a bath, redressed, and discarded crucial evidence like blood-stained clothes, the Marlin rifle and cartridges on his way to work as usual.

Thirteen Months later...

In December 1975, George and Kathy Lutz and Kathy's three children moved into 112 Ocean Avenue, a large Dutch Colonial house in Amityville, a suburban neighborhood located on the south shore of Long Island, New York. After 28 days, the Lutzes left the house, claiming to have been terrorized by paranormal phenomena while living there.