NEW YORK (CNN/Money) - Ex-Enron Chairman and CEO Kenneth Lay surrendered to authorities Thursday after being indicted in what experts called the centerpiece of the government's crackdown on the scandals that have rocked corporate America.

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In the 11-count indictment, Lay was accused of lying to the public, investors and Enron employees in charges that include securities and wire fraud and making false statements.

He pleaded not guilty to all charges and was released on $500,000 bail.

In a related move, the Securities and Exchange Commission accused Lay in a civil complaint that seeks more than $90 million. It also seeks to bar him from serving as an officer or director of a public company.

Lay appeared at the FBI office in Houston early Thursday and was led away to the federal courthouse with his hands cuffed behind his back.

At a news conference Thursday afternoon, Lay said he took responsibility for Enron's collapse but denied that he did anything wrong.

"I continue to grieve, as does my family, over the loss of the company and my failure to be able to save it," said Lay, speaking forcefully. "But failure does not equate to a crime."

Legal experts said the government has at last reached the pinnacle of its recent crackdown on corporate crime.

"Ken Lay was the big fish," said Orin Snyder, a former federal prosecutor. "This will be the showcase trial for the government in its war on fraud in the corporate boardroom."

Enron filed for bankruptcy on Dec. 2, 2001, after investigators found it had used partnerships to conceal more than $1 billion in debt and inflate profits. The company once ranked as the country's seventh largest.

The Houston-based company's collapse was the first of several high-profile scandals at some of the country's top corporations, among them WorldCom, Global Crossing, Adelphia Communications and Tyco International.

The case against Lay, however, "is the one everyone will look at -- more than Tyco and more than Martha Stewart," said Snyder, now a partner in Manatt, Phelps and Phillips. "This is even bigger than Adelphia."

At a press conference Thursday afternoon, James Comey, the No. 2 official at the Justice Department, called the investigation by the Enron Task Force, which marks its second anniversary Friday, "one of the most challenging and complicated matters that we have dealt with." The clear message, he said, to corporate America is that "no one is above the law and that no scheme of fraud is too complex" for government watchdogs to pursue.

Lay, 62, guided Enron for 15 years, shaping the once-obscure pipeline company into a world-leading energy trading concern. In bringing charges against him, prosecutors have finally reached the highest, if not the final, rung at the fallen energy giant.

Former Enron CEO Kenneth Lay being led in handcuffs to the U.S. courthouse in Houston Thursday.

Several former Enron executives, including former Chief Financial Officer Andrew Fastow, have pleaded guilty and agreed to cooperate with the government. Ex-CEO Jeffrey Skilling pleaded not guilty in February to fraud, insider trading and lying about Enron's finances.

Throughout their 2-1/2-year probe, government lawyers have tried to paint a portrait of a vast conspiracy in the upper echelons of Enron management, where top officials worked side-by-side to manipulate Enron's books and earnings.

To emphasize the claim of a widespread scheme, the charges filed against Lay were added to a pending indictment against Skilling and Richard Causey, Enron's former chief accounting officer. Skilling and Causey were expected to go to trial early next year.

In a 65-page "superseding" indictment against Lay and his two former deputies, prosecutors zero in on Lay's actions in the months leading up to Enron's collapse and after Skilling had abruptly resigned.

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It was at that time that Lay, according to prosecutors, took over the conspiracy that Skilling and Fastow had led to hide Enron's deteriorating balance sheet from the public eye. Even as Enron was rapidly crumbling, Lay repeatedly reassured employees and the financial community about the company's health at the same time he was quietly unloading his own Enron stock.

Lay, according to the indictment, sold 918,000 shares of Enron stock from August through the end of October 2001, the period during which he was urging employees not to panic. In one all-employee meeting, according to the indictment, Lay told Enron's 28,000 employees that "[o]ur liquidity is fine. As a matter of fact, it's better than fine, it's strong."

Ex-Enron Chairman Ken Lay talks about his 'tragic day,' his indictment and the fall of his company. Play video (Real or Windows Media)

Unlike Skilling and Causey, Lay was not charged with insider trading. But he was accused of defrauding three banks, including Bank of America (BAC: up $0.25 to $84.17, Research, Estimates), to obtain lines of credit that he illegally used to buy stock using loans from his brokerage account.

In recent days, as rumors spread that an indictment was near, Lay and his defense lawyers mounted a public campaign declaring his innocence in the hopes of warding off criminal charges. Lay has argued that he knew nothing of the secret partnerships managed by Fastow.

At his Thursday press conference, Lay insisted that his sales of Enron stock were made to meet margin calls, which are demands to pay back loans made to buy the stock, that kicked in as Enron's stock price dropped in late 2001. Lay noted that he tried to do everything he could to hold onto his Enron shares, including using a $10 million company bonus, instead of stock, to pay down debt.

Ken Lay's attorney, Mike Ramsey, comments on the former Enron chairman's indictment. Play video (Real or Windows Media)

He reiterated that he fully believed in the company's long-term viability when he urged employees to hold onto their Enron shares.

"I sold as little of my stock as possible to satisfy the calls because I was convinced it would increase in value," Lay told reporters.

Kirby Behre, a former federal prosecutor who is now in private practice in Washington, said late Wednesday. after news of the indictment broke. that it came as no surprise that Lay had been charged. "The government seems to have successfully worked its way up the food chain and enlisted the help of senior officers of the company who obviously were cooperating."

But the long lapse between Enron's bankruptcy and the indictment has caused some former federal prosecutors to question the strength of the government's case against Lay. The delay also caused critics to question whether Lay's once-close ties to President Bush were somehow insulating him.

White House officials have long tried to distance the president from Lay. Comey, responding to a question about any White House role, said "the decisions in this criminal case have been made under my leadership...and only there."

Legal experts pointed to ex-CFO Fastow as the likely missing link who gave the government the inside information it needed to bring the indictment. In exchange for his cooperation, Fastow was sentenced to 10 years in prison.

"I don't think Fastow would have gotten the plea offer he did unless he had something to deliver on Ken Lay," said Behre, now a partner in Paul, Hastings, Janofsky & Walker.

Michael Ramsey, the lawyer for Lay, indicated during a Thursday morning press conference that he too thinks Fastow's cooperation led to the final charges.

"Andy is absolutely a liar and a thief," said Ramsey.

Noting the on-again, off-again negotiations that led prosecutors to cut a plea deal with Fastow's wife, Lea, who was ultimately sentenced to one year in prison for tax evasion, Ramsey suggested that the "enormous pressures" on Andrew Fastow to protect his family will become part of Lay's defense strategy.

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He said the documents in the case will prove Lay's innocence.

"In our system, unfortunately, the people who get to determine whether someone is telling the truth or not have a dog in the fight," said Ramsey, referring to testimony from cooperating government witnesses who may be looking to save their own skin. "I don't think it's quite fair but that's the system."

Lay's indictment follows the filing of criminal charges against other former high-flying executives, including Bernard Ebbers of WorldCom, Richard Scrushy of HealthSouth, Dennis Kozlowski of Tyco and Enron's Skilling.

To date, the federal government has launched 31 separate prosecutions related to Enron's implosion, including a criminal case that brought down auditor Arthur Andersen two years ago and probes of about 20 former Enron employees. Of those, 10 have resulted in guilty pleas. The case against Arthur Andersen, which ended in a conviction, is the only Enron prosecution to go to trial so far.  

-- CNNfn's Jen Rogers contributed to this report