Huguette Clark, 104, the heiress to a Montana copper fortune who once lived in the largest apartment on Fifth Avenue, died Tuesday at a Manhattan hospital even as an investigation continues into how her millions were handled. Ms. Clark spent the last two decades of her life in New York hospitals.

She died "with dignity and privacy," her attorney, Wallace Bock, said in a statement.

The Manhattan district attorney is looking into claims made by Ms. Clark's family that she was kept isolated from almost everyone except Bock and her accountant and that she might not have understood decisions being made related to her fortune.

Ms. Clark was born in 1906 to a then-67-year-old U.S. senator, William A. Clark of Montana, and a 28-year-old Michigan woman named Anna Eugenia La Chapelle. Clark had made a fortune in mining and was one of the richest men in America. He built railroads across the United States, founding Las Vegas in the process.

Huguette Clark's fortune is believed to be worth some $500 million. As of last year, she still owned a 42-room, multifloor apartment at 907 Fifth Ave.; a Connecticut castle on 52 acres; and a Santa Barbara, Calif., mansion built on a 23-acre bluff overlooking the Pacific Ocean.

Beginning in the 1960s, Ms. Clark rarely left her Fifth Avenue home, having whatever she needed delivered.

- AP