Federal authorities say a stock trader and a lawyer, working with a middleman, made millions by using advance knowledge of mergers and acquisitions gleaned from the computers of prestigious New York law firms.

With confidential information plundered from some of New York's most prestigious law firms, a corporate finance attorney, a Wall Street trader and a "middleman" bought hundreds of thousands of shares in companies about to be acquired, selling them when the deals were done to net millions of dollars in instant profit, federal officials allege.

After each haul — totaling at least $32 million over nearly 17 years, according to federal investigators — the men met in Atlantic City casinos, where they believed they could share their large cash spoils without attracting attention.

But on Wednesday, in one of the biggest insider trading cases to date, authorities arrested the lawyer and the trader. No charges have been filed against the unnamed middleman.

The two arrested men, Matthew H. Kluger, a Washington, D.C., attorney, and Garrett D. Bauer, a professional stock trader, have each been charged with more than a dozen counts of securities fraud, money laundering and obstruction of justice. They also face insider trading charges from the Securities and Exchange Commission.