The Enron Task Force's (search) move to keep alive its 2 1/2 year investigation shows the government intends to press on for any overlooked documents or witnesses to strengthen its case against former Enron chairman Kenneth Lay (search), legal experts said Friday.

The Task Force, formed just weeks after Enron Corp.'s (search) bankruptcy filing in December 2001, has indicted 31 former Enron employees and others linked to the company's downfall, and reached Enron's highest echelon on Thursday with the 11 criminal counts lodged against Lay.

"I think it keeps a certain amount of pressure on the defendants," said Fred Fox, a lawyer in New York whose firm is involved in civil litigation against Enron.

"You always want to seal your case up as much as you can," he added.

Made up of dozens of prosecutors, FBI agents and IRS officials, the Task Force methodically worked up the chain of command, securing plea deals and cooperation from several former Enron employees, including former Chief Financial Officer Andrew Fastow (search), that is being used to implicate Enron's most senior leaders.

Even with indictments against Lay and former chief executive Jeffrey Skilling (search), that work will continue, U.S. Department of Justice Officials have said.

"We have gotten to the top of Enron's collapse, but we haven't necessarily gotten to the bottom," James Comey, deputy U.S. Attorney General, said in Washington on Thursday.

Holding the investigation open, and keeping the grand jury convened well into its third year, allows the government room to build on its case.

"It enables them to use the powerful tools they can bring to the grand jury process," said George Newhouse, a lawyer specializing in white collar crime defense and a former federal prosecutor.

Those tools, such as subpoenaing witnesses and documents and offering immunity to potentially key players, could help the government prove the difficult cases against Lay and Skilling, who are charged under an indictment that includes former company treasurer Richard Causey.

"It's also an implicit signal that they may not be 100 percent ready for Lay's trial," Newhouse said.

The ongoing investigation could also target Enron's board of directors, which failed to halt the accounting misdeeds that eventually triggered a liquidity crisis that brought the company down.

But experts said the board — which once included former head of the Commodity Futures Trading Commission (search) Wendy Gramm, the wife of former U.S. Senator Phil Gramm — would be even harder to link to the crimes than Lay.

"There is one more level up, the board of directors, but I don't think they're going to go there," said Nancy Rapoport, dean of the University of Houston's Law Center.