TD Bank, a unit of Canadian banking giant TD Bank Financial Group , is facing accusations from customers that the bank allowed their accounts to be emptied without their approval. Investors allege the bank's actions may have helped Florida attorney Scott Rothstein carry out a possible fraud.

Mr. Rothstein, the former chairman of a 70-lawyer firm in Fort Lauderdale, Fla., started a business to sell court settlements to investors at a discount, according to investors, who say they paid cash upfront in exchange for the right to recover the full amount of a court settlement at a later date. Investors, however, allege that Mr. Rothstein sold settlements that didn't exist, according to court papers in which his firm asked to be dissolved by the court.

Further details about the nature of the alleged fraud also came to light Wednesday, including the possibility that the business venture had been in place about three years. Mr. Rothstein and his attorney didn't answer a request for comment.

Mr. Rothstein created accounts at a Fort Lauderdale branch of TD Bank to hold funds from investors in Mr. Rothstein's settlements business, according to Stuart Rosenfeldt, a co-founder of Mr. Rothstein's law firm. Mr. Rosenfeldt says the accounts held about $500 million as recently as Oct. 23 but had a zero balance by Oct. 30.

The U.S. attorney's office in Miami is currently investigating Mr. Rothstein, according to a spokesman for Mr. Rothstein's law firm, Rothstein Rosenfeldt Adler P.A., which is cooperating with authorities.