HOUSTON -- The first witness has testified in the Houston trial of Enron's former top two executives accused of fraud and conspiracy.

The former chief contact for investors is cooperating with prosecutors after pleading guilty in 2004 to aiding and abetting securities fraud.

Mark Koenig described company founder Kenneth Lay and former CEO Jeffrey Skilling on Wednesday as heavily involved in running the company, which collapsed in scandal in December 2001.

Koenig also testified that Lay and Skilling considered Enron's stock price "very important."

He said they also didn't like the few Wall Street analysts who weren't bullish on the stock before Enron crashed.

Thousands lost their jobs, and investors lost billions when Enron went bankrupt in 2001.

Lay and Skilling seek much more than a "not guilty" in the government's premier criminal trial to emerge from the company's stunning collapse.

They want to exonerate Enron, too.

Their lawyers are asserting steadfastly that the two have committed no crimes, didn't look away while Enron's books were cooked, and didn't create a corrupt, greedy corporate culture.

But defense lawyers also told jurors on Tuesday that, "there's no evidence any books were cooked at Enron."

Skilling attorney Daniel Petrocelli told jurors that the case against his client and Lay isn't "a case of hear-no-evil, see-no-evil." He said -- "This is a case of there was no evil."

Lay attorney Michael Ramsey said his client and Skilling were energy trading pioneers who deeply loved a company felled by an acute crisis of market confidence.

But federal prosecutor John Hueston told jurors Lay and Skilling repeatedly lied to maintain Enron's polished image of success when they knew its heady profits and growth were illusory.

Hueston portrayed the Enron collapse as a case of "lies and choices."

Enron was once the nation's seventh-largest company.

Before 2001, it was considered an innovative new-economy maverick and admired as a top stock performer. But a spectacular collapse left thousands jobless and slammed Wall Street with billions in losses.

A former Enron pipeline worker who lost his job in the 2001 collapse said the trial "is what we've been waiting for."

Among the former employees who lost their retirement savings is Charles Prestwood. His nest egg contained $1.3 million, the sum total of working for Enron and its predecessor for 33 years. After the implosion, Prestwood's retirement savings fell to $3,600.

Prestwood said he is convinced that both Lay and Skilling knew everything that was going wrong.

"A lot of people said, 'Well, maybe they didn't know anything about it.' I said, 'You'll never convince me of that because the boss hog knows all of its piglets,'" Prestwood told KPRC-TV in Houston.

Skilling faces 31 counts of fraud, conspiracy, insider trading and lying to auditors for allegedly lying about Enron's financial strength.

Lay faces seven counts of fraud and conspiracy for perpetuating the alleged scheme after Skilling resigned in August 2001.

The trial is expected to last four months.

Both men have pleaded not guilty.

If convicted, each could face decades in prison and millions of dollars in penalties.