The case inspired the book and film versions called "The Amityville Horror."
DeFeo murdered his father, mother, two brothers, and two sisters in their Suffolk County home.
He initially blamed the shooting deaths of his 6 family members on a mob hitman but eventually confessed to carrying out the crime.
DeFeo died Friday at Sullivan Correctional Facility in Fallsburg, where he was serving six 25 years to life sentences.
The cause of death was not immediately known.
He was 69.
MORE NEWS: Police officers rescue children from burning home in Rockland County
Police officers rescue children from burning home in Rockland County
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