A prison officer found John Esposito unresponsive in his cell at Sing Sing on Wednesday, said spokeswoman Linda Foglia. The death is under investigation but does not appear to be suspicious, she said.
Esposito was serving 15 years to life for kidnapping Katie Beers and hiding her under his Bay Shore, Long Island, home in 1992.
Beers is now a married mother of two who earned a degree in business management and works in insurance sales near her home in rural Pennsylvania.
Her kidnapping attracted nationwide attention in early 1993, when revelations surfaced while she was still missing that she had suffered years of neglect from her mother and had been repeatedly sexually assaulted by her godmother's husband since she was a toddler.
On the 20th anniversary of her ordeal she co-wrote a book "Buried Memories: Katie Beers' Story."
Esposito, a family acquaintance, admitted to detectives on Jan. 13, 1993, that he had kidnapped Beers and showed them the dungeon. Beers was placed in foster care and raised in a comfortable East Hampton home with four siblings.
The county medical examiner will determine the cause of Esposito's death.
He had appeared before the parole board earlier Wednesday but Foglia said, "we don't know the decision." It was his fourth board appearance in 20 years in prison, she said, adding that he had a satisfactory prison record.
Beers said in a statement to CBS-TV in New York that she is happy Esposito will "never have the opportunity to hurt anyone ever again."