Refco shareholders have expanded their finger-pointing against the brokerage’s business partners for their alleged role in contributing to the firm’s 2005 collapse. On Monday, the shareholders filed a lawsuit against Refco’s former lead counsel, Mayer Brown LLP, and Joseph Collins, one of its senior partners.

The firm is also facing a similar lawsuit by Refco trustees that was filed earlier this year. The trustee suits—filed in Refco’s home state, Illinois—and the shareholder class-action suit—filed in the U.S. District Court for the Southern District of New York—accuse Refco’s business partners of partaking in a scheme to hide the company’s uncollectible debt. In addition to Mayer Brown, both suits name auditor Grant Thornton, Credit Suisse Securities, Banc of America, Deutsche Bank Securities, and others as defendants.

Totaling 108 pages, this most recent complaint against Mayer Brown suggests the law firm helped Refco conceal $430 million of debt by preparing and editing Refco’s “misleading” financial statements and other disclosures aimed at investors. The commodities brokerage filed for Chapter 11 protection in 2005, one week after disclosing its hidden debt and two months after its initial public offering. The company has since fallen apart.

A representative for Mayer Brown sent CFO.com a written statement saying the firm is in the process of looking at the complaint and plans to defend itself “with vigor.” The firm also took issue with the basis for the shareholders’ complaints against it, saying, “We believe that the securities laws do not permit shareholders to bring a claim, in the circumstances alleged here, against an outside adviser where the company allegedly misrepresented its financial position.”

Collins, the suit says, was Refco’s lead contact at Mayer Brown and considered Refco one of his clients for more than a decade. Collins works in the firm’s New York and Chicago offices and specializes in futures, securities, and derivatives law, according to the firm’s website. He did not respond to CFO.com’s request for comment.

The shareholders allege that Collins and other Mayer Brown attorneys worked with Refco CEO Philip Bennett “in devising, documenting, and concealing the massive fraudulent scheme that was intended to, and did, result in the false financial statements on which investors innocently relied” in return for tens of millions of dollars in legal fees. Bennett and former CFO Robert Trosten have been indicted on several criminal charges, including bank fraud, money laundering, and defrauding the purchasers of $600 million in notes.

According to the shareholders’ claims and the indictments, Refco hid its losses by transferring debt to a shell company controlled by Bennett called Refco Group Holdings Inc. In 1997, for example, Mayer Brown allegedly helped Refco document a transfer of at least $70 million in uncollectible debt by making it appear as though it was sold to RGHI, which would later seemingly repay that money. These types of transactions—made in the days before the end of a financial period —would make it appear as though Refco had a collectible receivable from a third party on its books.

“There is only one rational inference as to why the transfer was made: to fraudulently remove the problematic debt from Refco’s books and replace it with one that appeared collectible,” claim the shareholders, who are led by lead plaintiff Pacific Investment Management Co. The suit includes investors who owned Refco common stock and bonds from mid-2004 to October 2005.