He was 72.
Corrections spokeswoman Sue Bensinger said du Pont was found unresponsive in his Laurel Highland State Correctional Facility cell in Somerset County Thursday, The Philadelphia Inquirer reported. Bensinger said he had been ill for some time.
Du Pont, described as a paranoid schizophrenic during his trial, was sentenced to 13 to 30 years in prison in 1997 for the shooting death the previous year of Schulz outside his home. Schulz, a 1984 gold medalist, had been living on the du Pont estate in Newtown Square where his wife was head of security. No motive for the shooting ever was developed, Wikipedia reported.
Du Pont locked himself in his mansion for two days after the shooting, negotiating with police by telephone.
He was convicted Feb. 25, 1997, of third-degree murder but mentally ill.
Schulz's widow and children received a multimillion-dollar settlement as a result of a wrongful death lawsuit, Wikipedia said.
Du Pont recently lost an appeal arguing a motion sickness drug he had been taking might have worsened his mental state. The prosecution had argued he had been taking cocaine.
Du Pont, who earned a zoology degree from the University of Miami in 1965 and a doctorate in natural science from Villanova in 1973, was born Jan. 1, 1919, in Philadelphia to William du Pont Jr. and Jean Liseter Austin.