List died 2:30 p.m. Friday, four days after being taken to St. Francis Medical Center in Trenton from nearby New Jersey State Prison, said Deirdre Fedkenheuer, a spokeswoman for the state Department of Corrections.
No cause of death had been determined, pending an autopsy, Mercer County spokesman Pete Daly said.
List was convicted in 1990 of murdering his wife, Helen, 46; mother, Alma, 84; and three teen children by shooting them in their Westfield home on Nov. 9, 1971. He left town and due to meticulous preparations by List, it was more than a month before the bodies were discovered in the 18-room mansion.
In a letter he left for the pastor of his Lutheran church, List said he shot his victims from behind to spare them knowledge of what was happening until the last moment.
Because of a struggle, List wrote, he had to shoot John List, 15, repeatedly. Police said John was shot at least 10 times by .22-caliber and 9mm handguns. Also killed were Patricia, 16, and Frederick, 13.
In a postscript, List wrote, "Mother is in the attic. She was too heavy to move."
After the slayings, investigators found that List had two mortgages on his house, was failing as a financial consultant and had been siphoning money from his mother's $200,000 savings account.
He was arrested in June 1989 in Midlothian, Va., a Richmond suburb, where he had been working as an accountant.
Appeals of his convictions failed, including one asserting that he deserved a new trial because he suffered from post-traumatic stress disorder stemming from service in World War II.
