NEW YORK (CNN) -- He's wanted for bilking his former clients out of hundreds of millions of dollars.

Samuel Israel III pleaded guilty to stealing more than $450 million from his clients of Bayou Hedge Fund.

But did Samuel Israel III kill himself or fake his own death to escape a 20-year prison sentence? That's what authorities in New York are trying to figure out after he disappeared this week.

Israel, who co-founded Bayou Hedge Fund, pleaded guilty in 2005 of stealing more than $450 million from his clients. For the past three years, he's been out on bail and cooperating with prosecutors to help them recover some of the money.

He was supposed to report to prison Monday in Massachusetts to begin a 20-year sentence. Police said Israel left his home in Armonk, New York, about an hour outside Manhattan, about 9 a.m. and told his live-in girlfriend, "I'm driving to prison."

Israel's 2006 GMC Envoy was found about 12:30 p.m., parked on the Bear Mountain Bridge, high above the Hudson River in upstate New York. Authorities said the keys were in the ignition, but Israel was nowhere to be found.

Investigators are trying to determine whether he left what could amount to a suicide note scrawled in the dust and pollen on the hood of his car: "Suicide is Painless." The phrase is the name of the theme of the "MASH" television show, which also played during a fake suicide in the original movie.

With no other clues, investigators began trolling the Hudson River in search of Israel's body.

"We'll continue to search, if it takes a week, a month, you know, the rest of the summer," said Sgt. Dennis Stoll of the Rockland County Sheriff's Department.

Israel, 48, grew up in New Orleans, Louisiana. His father was a trader and the family was wealthy. He was divorced. Those who knew him describe him as charismatic. He was not in the best physical health; he wore a pacemaker and had endured nine back surgeries.

Ross Intelisano, an attorney representing 20 former clients of Bayou Hedge Fund who collectively lost $25 million, said Israel considered his 20-year prison sentence a death sentence and didn't expect to live that long.

"The former employees I spoke to said he wouldn't last a day in jail. So I don't know if he has the makeup to sit 20 years in jail," Intelisano said. "I think he's been living sort of a lie for so long, that I don't think it's that much a stretch for him to potentially put on this ruse, if that's what it is, and just try to escape."

Israel's attorney did not return calls from CNN.

U.S. Attorney Michael Garcia, apparently doubting that Israel committed suicide, has issued a warrant for his arrest. The FBI and U.S. Marshals haven't ruled out any possibilities. The Marshals are reportedly questioning a possible getaway driver who was seen on the bridge.

A spokesman for the New York state bridge authority said there are four security cameras on the bridge that are not monitored and are not very sophisticated. In fact, CNN has learned that the cameras might not be good enough to tell the difference between a car and a truck, let alone detect a person jumping off the bridge.

This isn't the first time authorities have investigated a possible suicide in the Bayou Hedge Fund case. When the fraud was exposed, Israel's business partner, Dan Marino, left a suicide note. He called it a "combined confession and suicide letter."

In the end, Marino didn't take his own life. He is serving a 20-year sentence for fraud, in the same prison where Israel is supposed to be.