Fallsburg, New York – Convicted "Amityville Horror" killer Ronald DeFeo Junior, who in 1974 shot and killed his parents and four younger siblings inside their Long Island home in a grisly case that inspired a book and a movie, has died in prison, officials said. He was 69.

DeFeo was serving a 25 years-to-life sentence at Sullivan Correctional Facility in upstate Fallsburg when he died Friday, according to a Department of Corrections spokesperson.

He was transferred to Albany Medical Center and pronounced dead at 6:35 PM. An autopsy will be performed to determine the official cause of death, officials said.

DeFeo was eligible for a parole hearing in July, according to state records.

He was convicted on six counts of second-degree murder for the killings, which took place on November 13, 1974, inside the five-bedroom Dutch Colonial-style home on Ocean Avenue in Amityville where he lived with his family.

Prosecutors said the 23-year-old DeFeo, the oldest son, used a .35-caliber rifle to shoot his mother, father, two sisters and two brothers while they were sleeping. His youngest brother was 9.

DeFeo initially blamed the murders on a mob hit man, but eventually confessed to carrying out the crime himself, claiming he heard voices saying his family was plotting against him.

"Once I started, I just couldn’t stop," he said during his confession, according to cops. "It went so fast."

"Hearing voices" was the basis of an unsuccessful insanity defense. After his conviction, a Suffolk County judge gave DeFeo six 25-years-to-life sentences.

The murders inspired the 1977 book The Amityville Horror and a cult film two years later by the same name starring James Brolin, Margot Kidder, and Rod Steiger.

The book and the movie focused on the Lutz family, who moved into the house several years after the murders and claimed they had been terrorized by paranormal phenomena while living there. They fled their dream home after 28 days.