Marc S. Dreier knew the 45th-floor conference room of Solow Realty well. He had been in it many times as a trusted lawyer for the company’s founder.

So nothing seemed amiss when he showed up one afternoon in October and told a receptionist he had a meeting with her boss, people associated with Solow say.

Mr. Dreier was elegantly dressed, as always, the people said. He had three people with him. The receptionist ushered the group past her desk. They were sitting there, visible inside the glass-walled room, a few minutes later when the boss, Steven M. Cherniak, happened to walk by.

Mr. Cherniak would later tell people at the company how surprised he had been to see Mr. Dreier. He had not scheduled any meeting with him, and he had no idea what Mr. Dreier was up to.

But people there gave little thought to Mr. Dreier’s odd visit until November, when the company’s founder, Sheldon H. Solow, received a disturbing call. The caller wanted to let Mr. Solow know that Mr. Dreier had offered him the chance to buy promissory notes that had been issued by the company, people associated with the firm said.

They were fake notes, and shortly thereafter, lawyers for Solow Realty — different lawyers — were in touch with federal authorities, reporting their suspicions that Mr. Dreier might be engaged in financial fraud.

Since that opening tip, federal authorities have been tracking what they describe as a brazen swindle of some of New York’s savviest investors by one of New York’s more accomplished lawyers. Mr. Dreier has been charged with multiple frauds in the United States and a related crime in Canada, and is being held without bail in Manhattan.

In court last week, prosecutors said their count so far put the money missing at $380 million, most of it lost by hedge funds and other investors who had bought promissory notes that were flat-out fictions.

In recent days, Dreier L.L.P., the Park Avenue law firm that Mr. Dreier founded, has been plunged into chaos. At least $35 million in escrow that was to have been held by the firm seems to be missing, the authorities say, and nearly all of its 250 lawyers are now looking for work.

The amounts pale next to the $50 billion fraud that another high-profile New York figure, Bernard L. Madoff, was accused last week of orchestrating, but they have unnerved lawyers and their clients in the broader legal community.

As the Dreier firm’s lawyers rummage through the law firm’s books, which had been until recently Mr. Dreier’s exclusive preserve, they are finding that bills have not been paid in months. Their health insurance is in default and the firm will not be able to make its $2.6 million payroll on Monday, lawyers there say.

“No one is in charge,” Vincent F. Pitta, a lawyer at the firm, complained last week in an affidavit in support of a government request to freeze assets. “The news of Mr. Dreier’s arrest has had a neutron-bomb-like effect on Dreier L.L.P.”

Few have fallen as quickly as Mr. Dreier, a Yale graduate and Harvard-educated lawyer who had been a partner at some of New York’s better known firms before opening up a high-profile practice of his own in 1996 that now has offices in five cities.

“He promised lavish salaries and lavish compensation and he was attracting the best and the brightest,” said Gerald L. Shargel, Mr. Dreier’s lawyer. Mr. Shargel said Mr. Dreier is cooperating with the receiver now running the firm.

The expense of running such an operation does not provide a ready explanation for thefts of such magnitude. Even the cost of sustaining Mr. Dreier’s appetite for luxury does not provide an easy answer for what instilled the desperation that seems to have prompted schemes involved here, schemes that prosecutors said involved Mr. Dreier pretending to be other people.

Mr. Dreier’s lifestyle includes a waterfront home in the Hamptons, a Manhattan triplex and a place on Ocean Avenue in Santa Monica, Calif. He kept a Mercedes 500 in New York, an Aston Martin in California, and a 121-foot blue and white Heesen motor yacht with a Jacuzzi and a crew of 10 docked in Manhattan or St. Maarten. Associates said the boat, the Seascape, was the site of late-night parties at which Mr. Dreier, who is divorced, was often joined by an attractive young crowd.

The law offices themselves at 499 Park Avenue were like modern art galleries. In court papers filed this week, the comptroller for the law firm reported that $30 million to $40 million of the firm’s assets had been spent on art. Among Mr. Dreier’s holdings were works by Picasso and a Warhol depiction of Jacqueline Kennedy Onassis.

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