NEW YORK (CNN/Money) - Federal authorities and investors are poised to seek millions in additional restitution from former Enron executives in the wake of a guilty plea by one of those executives.

Justice Department officials say the guilty plea Wednesday by Michael Kopper, a former assistant to ex-Enron Chief Financial Officer Andrew Fastow, should allow them to go after $23 million from Fastow and other former Enron executives. Kopper pled guilty federal charges of conspiracy to commit money laundering and conspiracy to commit wire fraud, the first charges brought in the high-profile Enron case.

AP photo

Fastow has been described as the architect of the limited partnerships that allowed Enron to hide millions in off-balance sheet debt from in investors. The charges that Kopper plead guilty to Wednesday charge that he, Fastow and others used the partnerships to misappropriate millions of dollars in undisclosed fees and illegal profits.

In addition, Fastow sold nearly $32 million in Enron shares and received $18.5 million in profit in the three years leading up to the collapse of the energy trader last fall, according to a study by Thomson Financial commissioned by CNN.

As part of his plea, Kopper agreed to cooperate with investigators and pay $12 million in restitution.

"This plea marks a significant milestone in the Enron investigation," Deputy Attorney General Larry Thompson said in a press conference. "We have secured the cooperation of an important witness, and...today's plea allows us to collect an additional $12 million to go to the relief of Enron investors."

Michael Kopper, a former Enron executive, pleads guilty to fraud charges in the Enron case and is released on $5 million bail. CNN's Ed Lavandera reports from Houston. Play video

But Kopper faces a lawsuit in Delaware Chancery Court over his role in another Enron partnership, known and LJM2, charging that a firm of his was advanced $3.9 million in management fees two days before his Jan. 4 ouster, according to a report in Thursday's Wall Street Journal. The paper said that LJM2's limited investors, who include major institutional investors such as J.P. Morgan Chase & Co., Merrill Lynch & Co., Citigroup Inc. and Canadian Imperial Bank of Commerce, are seeking restitution to the partnership.

The paper said Kopper (more about Michael Kopper) has denied wrongdoing and filed a suit of his own charging that the partnership has improperly withheld money due to him since his departure. The paper quotes lawyers for the partnership as saying they are unsure if his guilty plea Wednesday will change his position in their battle with him. Kopper's attorney in the Delaware case declined to talk to the media, the paper said.

After Kopper made his plea Wednesday, the Securities and Exchange Commission said it had also filed and settled civil charges against him, though Kopper did not admit or deny the SEC charges.

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As part of his bargain with the Justice Department and the SEC, Kopper will be barred from serving as an officer or director of a public U.S. company.

The SEC will handle the distribution of the $12 million, though it hasn't yet determined how it will disburse the money.

Kopper was released Wednesday on $5 million bond. The plea agreement must be approved by a federal judge, who will also have the discretion of sentencing Kopper to prison time. Kopper faces a total sentence of up to 15 years.

The Justice Department said it would make no recommendation to the judge about whether or not Kopper should be sentenced, though they would inform the judge of Kopper's cooperation. Officials with both Justice and the SEC expressed optimism about the amount of information Kopper would give them.

"We anticipate that the cooperation Mr. Kopper has agreed to provide will be important in identifying fully the individuals and entities that contributed to the company's collapse," SEC Enforcement Division Director Stephen Cutler said in a statement.

The criminal and civil charges accused Kopper of being involved in three transactions, called RADR, Chewco and Southampton, that allegedly helped Enron hide the true nature of its assets and liabilities.

Fastow spokesman Gordon Andrew would not comment on the charges. Fastow and Kopper had been called before the House Energy and Commerce Committee to answer questions about the Enron collapse, but both exercised their Fifth Amendment right against self-incrimination.

After the plea, Kopper's attorney said, "Michael has admitted he misused his position at Enron to enrich himself and others and in so doing violated his duties as an Enron employee."

Enron filed for bankruptcy protection in December after saying it had vastly overstated its financial results by hiding losses. The collapse of the No. 7 U.S. company was the first of several accounting scandals that sapped investor confidence and helped push stocks to five-year lows.

Last week, Sen. Byron Dorgan, D-N.D., chairman of the Senate Commerce subcommittee on consumer affairs, complained about the slow pace of the Enron investigation. He noted that executives from other companies, including bankrupt WorldCom, Adelphia Communications, Tyco International (TYC: Research, Estimates) and ImClone Systems (IMCL: Research, Estimates), had already been indicted.

Though pursuing federal charges against Enron and its former executives has been a somewhat laborious process, Thompson said the investigation was "active and ongoing" and that he was pleased with its progress.

"I think the American people would want the Department of Justice to conduct an investigation that is thorough and that produces charges that are sustainable in a court of law," he said.

Federal prosecutors have obtained convictions against former Enron auditor Arthur Andersen and a former Andersen executive, David Duncan.

Kopper, 37, is a native of New York's Long Island and a 1986 graduate of Duke University. He later attended the London School of Economics, where he finished in the bottom fifth of his accounting class. After a brief stint at Toronto Dominion Bank, he joined Enron in 1994.