A former eye doctor who set off a seven-year federal investigation into class action law firm Milberg Weiss has agreed to plead guilty to taking $6.4 million in secret kickbacks from the firm, lawyers in the case said on Wednesday.

Steven Cooperman, 64, of Connecticut will plead guilty to a charge of conspiring with Milberg Weiss and some of its partners to obstruct justice and make false statements in class actions the firm filed against scores of publicly traded companies between 1988 and 2003, federal prosecutors in Los Angeles said.

The firm and two of its senior partners have been indicted on charges that they participated in a scheme to pay secret kickbacks to Cooperman and other plaintiffs.

Milberg Weiss and its partners have pleaded not guilty.

That case is set for trial in 2008.

In a statement released on Wednesday, Milberg Weiss said the allegations against the firm "are not new" and "have never been credible and they are no more so today."

Cooperman first brought Milberg Weiss to prosecutors' attention after he was convicted in 1999 of federal insurance fraud charges for staging the theft of two paintings, a Picasso and a Monet, from his Los Angeles-area home.

Prosecutors gave Cooperman amnesty in the Milberg Weiss investigation in exchange for his cooperation in providing the government with information about the alleged kickback scheme.