HOUSTON -- Lawyers for former Enron Corp. chiefs Kenneth Lay and Jeffrey Skilling launched their case Monday with the two men's former assistant, who said she believed a key prosecution witness lied about his involvement in company-related crimes.

As they did during the first 2½ months of the fraud and conspiracy trial of the two former chief executives, defense lawyers sought to erode prosecution testimony with their first witnesses.

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Video: Ramsey's Medical Complication Could Delay Trial

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Joannie Williamson served as an assistant at various times to Skilling, Lay and former investor relations chief Mark Koenig, a key prosecution witness.

Koenig pleaded guilty in August 2004 to aiding and abetting securities fraud and testified for the prosecution that he lied to investors about Enron's finances. During more than seven days in the witness chair in February, he denied claims that he had told Williamson he pleaded guilty to a crime he didn't commit.

The defense teams maintain that most ex-Enron executives who admitted to crimes did so out of fear of prosecution and in hopes of receiving lenient punishments rather than because they broke the law.

Williamson said Koenig, whom she described as a close family friend as well as a former boss, called her the day he pleaded guilty.

"I said, 'You're not guilty,' and he said, 'I know that, but in order for this to work, everyone needs to believe that I am."'

She added she did not believe he was guilty, even though Koenig told jurors in February, "I pled guilty because I am guilty."

Williamson said yes when prosecutor Kathryn Ruemmler asked if she thought Koenig lied during his testimony, which implicated Lay and Skilling in a string of falsehoods.

"Did he tell you he was pressured?" Ruemmler asked.

"No, he did not," Williamson replied.

Skilling lawyer Daniel Petrocelli said Monday that Skilling could testify as early as Wednesday afternoon, depending on how long the first few defense witnesses take on the stand. Lay's testimony will come later.

Lay's lead lawyer, Michael Ramsey, was absent from the trial Monday, undergoing outpatient tests on a stent he had inserted in his chest on March 24. Lay spokeswoman Kelly Kimberly said the attorney will have "an invasive procedure" Tuesday during which doctors can evaluate the stent.

"It's 100 percent certain that he's going to have this procedure (Tuesday), but when exactly he makes it back, whether it be Wednesday, Thursday, Friday or even next week, on Monday perhaps, that's not clear," Petrocelli said.

"We are hopeful that he will be back at the trial soon," Kimberly said. The trial will continue despite Ramsey's medical condition.

Other defense witnesses who testified Monday included:

Scott Stoness, a former analyst for Enron's retail energy unit, Enron Energy Services. He was called to counter prosecution testimony from former unit Chief Executive David Delainey, who told jurors that in March 2001 he reluctantly agreed to a Skilling-approved plan to move part of the failing retail unit into a larger profitable division to hide $200 million in losses. Stoness said Enron didn't know until May whether it would have such losses, and they reached $170 million.
Diann Huddleson, another former EES analyst. Skilling's legal team called her to show that EES wasn't in disarray as Delainey and other government witnesses have said. She said she persistently chased California utilities to pay Enron for energy deliveries during that state's power crisis of 2000-2001 despite testimony from a former in-house accountant about a drawerful of uncashed checks for amounts that Enron's books claimed had been collected. The defense also sought to counter prosecution testimony that Enron wrongly raided reserves to pad earnings by showing through Huddelson that the company had another purpose for those funds. Huddelson noted Enron had reserves of up to $400 million to cover any losses from California utilities that failed to pay their bills.

Skilling could take the stand as early as Wednesday and his testimony could last up to a week. Lay would follow a short time later.

The government contends that Skilling and Lay repeatedly lied to investors and employees about Enron's strength when they knew the energy trading company was struggling with weak ventures and massive losses.

The defendants say no fraud occurred at Enron other than that committed by a few executives who skimmed millions from secret side deals. They say bad publicity and lost market confidence drove what was once the country's seventh-largest company into bankruptcy proceedings in December 2001.

Prosecutors rested their case last week.

Skilling faces 28 counts of fraud, conspiracy, insider trading and lying to auditors, while Lay faces six counts of fraud and conspiracy. Last week, U.S. District Judge Sim Lake approved prosecutors' request to drop three counts against Skilling and one count against Lay to streamline their case.