An autopsy was conducted Monday on 67-year-old Jeffry Picower, the day after he was found by his wife at the bottom of a pool at the couple's sprawling oceanside Palm Beach mansion.
He died a short time later at a nearby hospital.
Picower's body showed no visible injuries, said Joseph Sekula, spokesman for the Palm Beach Fire Department.
"There wasn't anything noted as far as trauma or anything to the body," he said.
Picower had been accused of making more than $7 billion off the investment schemes of Madoff, who is currently serving a 150-year prison sentence after he admitted losing billions of dollars for thousands of clients.
Some victims of Madoff's vast Ponzi scheme say Picower was the fraud's biggest beneficiary. In a lawsuit to recover assets, trustee Irving Picard demands he return the allegedly bogus profits.
Picower was No. 371 on the Forbes 400 list of the wealthiest Americans, with a net worth of $1 billion.
The non-profit journalism Web site ProPublica reports that "between December 1995 and December 2008, Picower and his family withdrew from their various Madoff accounts $5.1 billion more than they invested with the self-confessed swindler, according to a lawsuit filed by the trustee who is trying to recover money for those Madoff defrauded."
"In contrast, shortly after he confessed Madoff declared his household net worth to be between $823 and $826 million, according to court documents," the story continued. "While the Madoffs clearly lived opulently, no evidence has emerged that their combined assets and expenditures approached the amount the Picower family is alleged to have withdrawn from the scheme."
In the lawsuit to recover Madoff's assets, trustee Irving Picard demanded Picower return more than $7 billion in bogus profits. Irving Picard did not immediately respond to a phone message left at his office Sunday. Madoff's attorney, Ira Sorkin, also didn't respond to a request for comment.
Picower and his wife started the Picower Foundation in 1989, which has given millions to the Massachusetts Institute of Technology, Human Rights First and the New York Public Library. It also funded diabetes research at Harvard Medical School.
The foundation, whose assets were managed by Madoff, said in its 2007 tax return its investment portfolio was valued at nearly $1 billion.
After the Madoff scandal broke in December, the Picower foundation said it would have to cease grant-making and would be forced to close.
But the trustee's lawyer said Picower's claims that he was a victim "ring hollow" because he withdrew more of other investors' money than anyone else during three decades of investing with Madoff and should have noticed signs of fraud.
According to the lawyers, Picower's accounts were "riddled with blatant and obvious fraud," and he should have recognized that because he was a sophisticated investor.
Picower had asked that the lawsuit be dismissed, saying it was unsupported by the facts. Messages left for Picower's lawyer, William Zabel, and his wife's attorney, Marcy Harris, weren't immediately returned Sunday.