"I do not believe that this was a one-man show," said John Gillies, head of the FBI in South Florida.
At least four people in the Rothstein Rosenfeldt Adler firm met with investors or handled money, investors told the Sun Sentinel.
The investors also identified two people from a finance company in the same building as the law firm. The two people attended meetings and represented themselves as Rothstein's agent and broker, investors said.
Rothstein sold investors structured legal settlements in sexual harassment and whistle-blower cases that guaranteed a minimum 20 percent return, according to records he gave investors. The plaintiff would receive a discounted lump-sum payment from the investors, who would then collect the full settlement from Rothstein over several months.
Prosecutors now say the settlements never existed, and Gillies said Thursday that the alleged fraud could exceed $1 billion. No one, including Rothstein, has been charged.
Gillies declined to identify anyone as a Rothstein accomplice or say whether others could face criminal charges.
"As the investigation proceeds, I believe that's where the evidence will take us," he said.
Rothstein's partner, Stuart Rosenfeldt, has said he had "no clue" about the alleged fraud. The other partner, Russell Adler, is blameless and "totally without any liability," said his lawyer, Fred Haddad.
Here's a look at some of those who participated in some way in Rothstein's investments, according to investors. It's not clear whether they knew about any fraud or were duped along with investors:
David Boden, general counsel of the law firm, sat in on Rothstein's meetings with investors and represented him in follow-up calls and negotiations.
Potential investor Alan Sakowitz, a Miami lawyer, met with Boden and Rothstein three times and said Boden tried to dispel his doubts in an August phone call.
"I asked him, 'Is this for real?' He said it was, that it's a legitimate deal, that everything was aboveboard," Sakowitz said.
Another group of investors met with Boden about the same time, and he gave them his law firm business card, said their attorney, Daniel Serber, of Aventura.
"David Boden was the contact person," Serber said. "He was the attorney who was in charge of negotiating the structured settlement documents."
After investors did not receive their scheduled payments from Rothstein the last week in October, Serber visited the law firm the Friday before Halloween. Rothstein already had left the country, and Boden met with Serber.
Boden told him that "it's business as usual" and that Rothstein had gone to London and "was working on getting some issues resolved so that the payments could be made."
Rothstein himself sent an e-mail later that afternoon, saying he was in London and would "instruct the wires to be sent out on Monday," Serber said.