Federal prosecutors accused a high-profile South Florida attorney of concocting a Ponzi scheme that lured millions of dollars from investors with promises of big payoffs from legal settlements that never existed, according to court documents filed Monday.

The civil complaint, seeking forfeiture of eight pieces of property owned by lawyer Scott Rothstein, marks the first time prosecutors have leveled fraud allegations at him_ even though criminal charges have yet to be announced. It was filed the same day FBI and Internal Revenue Service agents seized luxury cars, boats, bank accounts and other possessions of the once high-flying Rothstein. The forfeiture complaint put the value of the real estate at more than $18 million.

In the complaint, prosecutors claim that Rothstein operated the Ponzi scheme since 2005 using his law firm, Rothstein Rosenfeldt Adler. Investors were promised fat profits of 20 percent or more by paying lump sums to people who had won legal settlements that would supposedly pay out larger amounts over a longer period.

It was all a lie, the complaint contends. Like all Ponzi schemes, new investor money was used to pay earlier investors to keep up an illusion of success, backed up by false documents showing bank accounts containing fictional large sums.

"The investigation has established that no such settlement agreements had ever existed and the entire investment scheme was a fraud," prosecutors said in the complaint. "The scheme involved hundreds of millions of dollars."

Rothstein's attorney did not respond to two phone messages seeking comment. The lawsuit mentions "others" involved in the scheme, but no one else is named.

The eight properties should be forfeited as ill-gotten gains of the scheme, prosecutors said.

Earlier Monday, FBI and IRS agents spent much of the day taking inventory at Rothstein's $6.4 million home _ one of those that would be forfeited _ where several of his luxury cars and boats were kept. Assets are typically seized in fraud investigations so they may later be sold to repay wronged investors.

The seizure warrants, described by a federal law enforcement official on condition of anonymity because of the ongoing investigation, are sealed in federal court. News photographers captured images of Rothstein's Ferrari being towed away by agents, and several were posted outside his ritzy home for much of the day.

One bank used by the law firm, Gibraltar Private Bank & Trust, issued a statement saying a deal involving a Rothstein company was put on hold. The Rothstein entity, Bahia Property Management LLC, had purchased 5 percent of Gibraltar, but the deal will be frozen pending the outcome of the investigation.