Federal prosecutors are preparing to bring criminal charges against former Enron Corp. Chief Financial Officer Andrew Fastow next week, sources familiar with the investigation said on Thursday.

The sources said fraud and possibly other charges were expected to be brought in a criminal complaint to be filed in federal court in Houston, most likely on Wednesday.

Fastow's one-time protege -- former Enron executive Michael Kopper -- pleaded guilty last month to money-laundering and fraud charges and agreed to cooperate with investigators as they examine the activities of higher-ranking executives.

Kopper was the first former officer of the collapsed energy trader to plead guilty in the Justice Department's long-running investigation. He implicated Fastow in three fraudulent deals involving Enron off-balance-sheet partnerships.

Massive losses from various Enron partnerships hid billions in debt, inflated profits, and sparked the company's fall into bankruptcy in December.

The Justice Department, investigating Enron since January, has been under growing political pressure to bring criminal charges against the company's former top executives. The collapse of Houston-based Enron was the first in a wave of corporate scandals.

A Justice Department spokesman declined to comment on the investigation. Fastow, through his representatives, has consistently declined to comment.