Jeffry Picower, a financier accused of profiting more than seven billion US dollars from the investment schemes of his longtime friend Bernard Madoff, was found at the bottom of the pool at his Florida oceanside mansion and died, police said. He was 67.
Picower's wife discovered his body and pulled him from the water with help from a housekeeper, authorities said.
He was pronounced dead at Good Samaritan Medical Centre.
Palm Beach police are investigating the death as a drowning, but have not ruled out anything on the cause of death.
Picower suffered from Parkinson's disease and had "heart-related issues," said family lawyer William D. Zabel. He described Picower's health as "poor".
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, adding that "it did appear that he was swimming because he was wearing swimming trunks".
Detectives were still at the home more than six hours after the initial emergency call.
The iron gate to his long driveway was open and several Palm Beach police cars were parked near the mansion. The home and property is worth more than 33 million US dollars, according to the county property appraiser's records.
Picower had been accused by jilted investors of being the biggest beneficiary of Madoff's schemes.
In a lawsuit to recover Madoff's assets, trustee Irving Picard demanded Picower return more than seven billion US dollars in bogus profits.
Mr Picard said "litigation will continue". Mr Zabel, the Picower family lawyer, said in a statement that "there was progress towards a settlement with the trustee".
Madoff is serving a 150-year prison sentence after he admitted losing billions of dollars for thousands of clients over a half-century career that saw him rise to be a Nasdaq chairman.
Jonathan Landers, an attorney representing a large group of victims, said it was impossible to tell what effect Picower's death would have on efforts to recover funds lost in Madoff's massive Ponzi scheme.
"While there are allegations regarding his knowledge of the Madoff fraud and his possible liability to investors, none have been proven," he wrote.