On the morning of November 13, 1974, six members of the DeFeo family were found shot in their beds at 112 Ocean Avenue in Amityville, New York. Among the dead was 12-year-old Marc Gregory DeFeo, born September 4, 1962, the fourth of five children. The other victims were Ronald DeFeo Sr., 43; Louise DeFeo, 43; Dawn, 18; Allison, 13; and John, 9.

Ronald DeFeo Jr., then 23 and known as Butch, was the sole survivor and was arrested and charged with six counts of second-degree murder. Prosecutors said a .35-caliber Marlin rifle was used. The defense argued he was insane and heard voices; the prosecution suggested a financial motive. On November 21, 1975, a jury found Ronald DeFeo Jr. guilty on all six counts; he received six concurrent sentences of 25 years to life. His statements about the case changed over time, at one point implicating his sister Dawn.