Michael Kopper, a former managing director of Enron Global Finance, pleaded guilty to wire fraud and conspiracy to commit money-laundering after signing a co-operation agreement with federal prosecutors.

The agreement will help prosecutors build a case against Fastow and other Enron executives who so far have not been charged with any crime.

Kopper ran several off-balance sheet partnerships set up by Fastow which were used to hide the true level of debt at the company.

The charges against Kopper identified Fastow as his partner in the illicit schemes.

In a statement made by the SEC, the regulator said Kopper would have to forfeit a total of $12m and had been barred from being an officer or director of a public company.

Kopper appeared in the same courtroom where two months ago Andersen, Enron's auditor, had been found guilty of obstruction of justice.