Lay, 64, faced the prospect of spending the rest of his life in prison after a Houston jury in May found him guilty of conspiring to inflate the energy company’s stock price and misleading investors and employees who lost billions of dollars in its 2001 bankruptcy. Friends said Lay, who looked grayer and thinner during his four-month trial but otherwise bore no outward signs of poor health, expected to be handcuffed and taken into custody immediately after his sentencing this fall.

Lay’s death all but ensures that defense lawyers will seek to throw out his criminal conviction — and casts serious doubt on the ability of the government and investors to recover money from the Lay estate, legal experts said. Barry Boss, a Washington lawyer not involved in the Enron case, said Lay’s death complicates prosecutors’ request Friday for a $43.5 million money judgment against him because it is not clear whether the government can seek restitution against someone who has died. “Under the prevailing case law . . . I don’t see any way they can proceed against Lay for restitution in the criminal case, or anything else for that matter,” said Boss of Cozen O’Connor.

Deputies from the Pitkin County, Colo., sheriff’s office were called to the rental property at 1:41 a.m. Mountain time to respond to a medical emergency. An ambulance took Lay to Aspen Valley Hospital, where he was pronounced dead at 3:11 a.m., a hospital administrator said.

Robert Kurtzman, a forensic pathologist who performed an autopsy on Lay’s body yesterday, said the immediate cause of death was coronary artery disease. At a televised news conference, he said there was “no evidence of foul play.” He added that Lay might have had a previous heart attack.

Joe DiSalvo, director of investigations for the sheriff’s office, said the results of a standard toxicology screen, which would pick up any unusual substance in Lay’s system, would not be available for a few weeks.

“He’s been under extraordinary stress for five years,” said pastor Stephen P. Wende of Houston’s First United Methodist Church after speaking with relatives, including some of Lay’s five children and dozen grandchildren. “I don’t think his spirit gave way, but his body did.”

Last night, the Lay family issued a statement saying they “are grieving the sudden loss of their husband and father.”

Lead defense attorney Michael W. Ramsey, who underwent two heart procedures to unclog his arteries during the trial, has yet to speak publicly about Lay’s death. But a source who spoke on condition of anonymity because family members had not authorized him to speak about the case said Lay’s defense team will undoubtedly cite legal precedents that allow defendants to vacate their convictions if they die during an appeal.

For instance, the U.S. Court of Appeals for the 5th Circuit two years ago tossed Andrew Parsons’s conviction on arson, mail fraud and money-laundering charges. A divided appeals court extinguished the conviction on two grounds: The justice system is wary of labeling defendants guilty if they have not had a chance to appeal, and it is loath to punish dead people or their estates.

Meanwhile, Trey Davis, a spokesman for the University of California, the lead plaintiff in a multibillion-dollar lawsuit lodged against former Enron executives, their investment bankers and accountants, said yesterday that he did not expect shareholders to continue to pursue civil claims against Lay. A Securities and Exchange Commission case against Lay continues, but it will be a more difficult battle if regulators can no longer point to Lay’s criminal conviction and must introduce reams of evidence anew.

Exactly how much money is in the Lay family coffers remains as much in dispute as the man’s legacy. Earlier this year, Lay testified during six sometimes-combative days that his personal debts had mounted to nearly $100 million in his final year at Enron. He told the jury that he and Linda, his second wife of two dozen years, had sold lavish properties in Aspen, Colo., and Galveston, Tex., but were still $250,000 in the hole. The dream he lived, Lay said, had become “the American nightmare.”

Six days ago, federal prosecutors sought to seize $6.3 million they said Lay was about to collect from an investment in a Goldman Sachs limited partnership fund. The government also wanted at least $1.5 million more that Lay had borrowed from Enron to pay off the mortgage on the 33rd-floor luxury condominium in Houston where he and his wife lived.