The Palm Beach Fire Department told ABC News that Picower had no pulse when fire rescue workers arrived at his oceanfront mansion after his wife called 911. She and his housekeeper pulled his body from the pool shortly after noon.
No one benefited more from the Madoff scheme that Picower, according to bankruptcy lawyers who sued him and alleged he had taken out $7 billion more than he had put in.
Click here to go behind the scenes of Brian Ross' investigation into Bernie and Ruth Madoff.
Investigators told ABC News.com that Picower would also have likely faced criminal charges.
Some investigators considered Picower to have been the actual mastermind of Madoff's massive con, or at least an equal "partner in crime."
"He made 30 times what Madoff did from the scam and about a third of the missing money went to Picower," said one of the investigators on the case Sunday.
Police said they did not yet know the cause of death.
"They need to do a full autopsy and set of toxicology tests," the investigator said.
Picower's attorney, William D. Zabel, told ABC News.com that Picower's death came as a total surprise to his family.
"This is a personal tragedy and the family is in deep grieving," Zabel said.
Zabel said Picower's legal team had been in active negotiations to settle the civil case and added that he had received no notification of any pending criminal charges.
Picower, a tax shelter lawyer and accountant, was not well known in financial circles until his name surfaced in the Madoff case in the past few months. His $7 billion profit stunned other Madoff
investors, many of whom lost their life savings.
Investigators say Madoff documents show that Picower regularly gave instructions for Madoff to create phony trades on his behalf so that he could withdraw billions.
The lawsuit brought by the bankruptcy trustee named Picower, his wife Barbara and the Picower Foundation, which gave generously to charities.
Palm Beach fire department authorities told ABC News that his wife saw her husband swimming in the pool only 15 minutes before spotting his body on the pool floor, and that Picower's wife rode in the ambulance to Good Samaritan Medical Center in West Palm Beach.
The hospital confirmed that Picower is deceased.