A surprise twist in the criminal case against Broadcom Corp. co-founder Henry Samueli again raises questions about plea bargains, one of the most important and controversial aspects of the justice system.

In a Santa Ana, Calif., court last week, federal Judge Cormac Carney dismissed the criminal complaint charging Mr. Samueli with lying to the Securities and Exchange Commission in its investigation of whether Broadcom misstated its earnings by improperly accounting for executive stock options. Judge Carney's dismissal came even though Mr. Samueli had stood before him in 2008 and pleaded guilty to that very crime.

Mr. Samueli did what lawyers and legal scholars fear a disturbing number of other people have done: pleaded guilty to a crime they didn't commit or at least believed they didn't commit. These defendants often end up choosing that route because they feel trapped in a corner, or fear getting stuck with a long prison sentence if they go to trial and lose.

The evolution of the criminal-justice system in recent decades has put many defendants "under all but impossible pressure to plead guilty, even if they're not," said Yale law Prof. John Langbein, a critic of the plea-bargain system.

The dismissal came immediately after Mr. Samueli testified before Judge Carney as a defense witness in the criminal trial of former Broadcom Chief Financial Officer William Ruehle, who was charged with fraud in the options-granting activities. Judge Carney then called him before the bench and said he was setting aside Mr. Samueli's guilty plea and dismissing the case against him.

The judge said he had concluded that while Mr. Samueli's answer to the SEC was "ambiguous, evasive and arguably nonresponsive," it wasn't materially false. Judge Carney later dismissed the charges against Mr. Ruehle.

Mr. Samueli signed the plea agreement believing he may have violated the law, but that belief was based on the prosecutors' distortion of the evidence, said his attorney, Gordon Greenberg. "The government put incredible pressure on" Mr. Samueli, he said. The U.S attorney's office declined to comment.

Experts say that many people find themselves in Mr. Samueli's predicament, though it is impossible to put a number on how many people plead guilty to crimes they may not have committed.

One reason for false pleas is that potential prison sentences, particularly on the federal level, have increased for many crimes. This has helped put more power into the hands of prosecutors, who decide what charges and how many counts to levy against a defendant. Generally, the more charges and counts, the more the potential prison time. If a defendant exercises his right to a trial, he or she faces all those counts. However, that same defendant can drastically cut the number of counts -- and potential prison time -- with a plea bargain.

In the Enron scandal, for example, former Chairman Kenneth Lay, former President Jeffrey Skilling and former Chief Accounting Officer Richard Causey were charged with fraud and conspiracy and set for trial together in early 2006. Shortly before the trial, Mr. Causey reached a deal with prosecutors, pleading guilty to one count of securities fraud, and was sentenced to 5 1/2 years. At trial, Mr. Skilling was convicted on 19 counts and received a more than 24-year sentence. (Mr. Lay was convicted on 10 counts but died shortly after the trial.)

Few plea bargains are ever seriously challenged. The Innocence Project at the Benjamin N. Cardozo School of Law specializes in using DNA evidence to find prisoners who have been wrongly convicted of murder or other serious crimes. The project has represented 17 defendants who pleaded guilty even though DNA evidence later proved their innocence, said co-director Peter Neufeld. "Our clients plead guilty, because if they go to trial and lose they could get a death sentence," he said. "They plead guilty to save their lives."

Alleged white-collar criminals don't face that danger. However, criminal jeopardy has increased in the corporate suites, sparked by public anger over business and financial scandals, say legal observers.

To be sure, it is widely agreed that the vast majority of those who pleaded are in fact guilty. And plea bargains are an essential part of the system, accounting for some 95% of all federal convictions, according to the most recent statistics. The government doesn't have the means to bring every defendant to trial.

"If every defendant in every county jail got off the chow line this morning and decided he or she wanted a jury trial, the system would implode," said Brice Wice, a Houston criminal-defense lawyer who specializes in handling appeals. Often, he said, it is defense lawyers, rather than prosecutors, who exert pressure to sign guilty pleas. "They tell their clients, take this or you'll get life," Mr. Wice said.

Write to John R. Emshwiller at john.emshwiller@wsj.com and Nathan Koppel at nathan.koppel@wsj.com

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