NEW YORK - The 104-year-old heiress to a Montana copper mining fortune - now a recluse in a New York hospital room - is at the center of a criminal investigation into her fortune and welfare, two people familiar with the probe told The Associated Press.

The Manhattan district attorney's office is looking into how Huguette Clark is being cared for and how her finances are being handled, according to the people, who spoke on condition of anonymity because they are not authorized to speak publicly about the probe.

Clark has been living in hospitals since leaving her luxury co-op overlooking Central Park more than 20 years ago, according to building staff who saw her leave in an ambulance.

Attorney Wallace Bock and accountant Irving Kamsler have been in charge of her financial affairs for years, and they're among the few people who have contact with Clark.

The Manhattan district attorney's office declined to say whether a probe was under way. The office successfully prosecuted the case surrounding Brooke Astor, the late philanthropist and heiress whose 85-year-old son was convicted of scheming with her attorney to bilk millions of dollars from her.

Clark is worth about half a billion dollars - four times as much as Astor.

There is no public record of a will, and distant relatives have not seen her in years.

In recent weeks, the Manhattan mystery has taken on sinister turns, with two men apparently crucial to the investigation - Bock and Kamsler, a registered sex offender convicted of e-mailing pornographic pictures to underage girls.

Neither has been charged in the Clark probe, but the questions remain: How are she and her fortune being cared for?

When she left home on the stretcher, Clarke was frail but not physically ill, according to building staff.

Since then, nobody has lived in her meticulously maintained 42 rooms at 907 Fifth Ave., or her Connecticut castle, surrounded by 52 acres of land and now on the market for $24 million.

The properties are financed by her inheritance as the daughter of a 19th century Montana copper mining king who built railroads across America, founding Las Vegas along the way.

Clark also owns a mansion in Santa Barbara, Calif., on a 23-acre bluff overlooking the Pacific Ocean.

All that's left of her privileged existence are the lifeless properties - and her name in the New York Social Register.

After leaving the Fifth Avenue apartment, Clark took up residence in Doctors' Hospital on the Upper East Side - to be "more comfortable," according to MSNBC.com reports documenting her life.

But the hospital building was razed in 2004, and she's now in an ordinary hospital room elsewhere in the city.

Huguette Clark's story begins in 1906 Paris, where she was born to then 62-year-old U.S. Sen. William A. Clark of Montana and a 23-year-old Michigan woman named Anna Eugenia La Chapelle.

Years of mining the Montana earth for copper made Clark the second-richest man in America, after the Rockefellers. To prove it, he built an ostentatious mansion on New York's Fifth Avenue and gained power - as a U.S. Senator serving a single term.

His daughter attended Miss Spence's School for Girls in Manhattan, now The Spence School, studying modern dance while getting savvy about politics and art.

In the Roaring Twenties, the Clarks' Fifth Avenue home was the scene of wild parties, and Huguette hung out with rich young men who drove fast cars and flew planes.

At 22, she married a poor bank clerk, but they parted ways after only nine months. Huguette Clark cited desertion by her husband. He claimed she failed to consummate the marriage, according to "The Clarks: An American Phenomenon," a book written by former family employee William D. Mangam.

Shortly after her father died in 1925, she and her mother left the mansion and moved to 907 Fifth Avenue, the Italian-Renaissance-palazzo-style building where Huguette Clark lived for six decades. It's still one of the city's most posh co-ops, and hers is the biggest apartment property on Fifth Avenue.

When her mother died in 1963, Huguette was transformed from a rather private socialite in her 50s to a social specter - an eccentric whom building staff members say they never saw; she had whatever she needed delivered.

Even distant relatives attempting to visit were discouraged from entering; she told several of them to stand on the sidewalk and she would wave to them, staffers remember.

"She never went out," said Laurance Kaiser IV, a Manhattan real estate agent who once met her in the Fifth Avenue building.

She apparently trusted almost no one, but was generous. Each doorman got a $500 check from her at Christmas. They'd seen her only a few times over the decades - and only by accident, while slipping mail under her door when she happened to open it. She would scurry away.

Huguette Clark left for good one day in the 1980s, on the stretcher.

"She just got tired of living," Kaiser said.

Steven Shirley, an amateur historian in Helena, Mont., said Clark was "very much on top of things - very lucid" when he last spoke to her a half dozen years ago, by phone.

Though hard of hearing and unable to understand all of his questions, "she reminisced about her days in France before World War I," Shirley told the AP. "She read the New York Times every day and she was very aware of world events," Shirley added.

In the end, her vast fortune allowed the heiress to lead an ever more solitary life.

She's said to have once told friends that extreme wealth is a "menace to happiness."