In the coming months, the political battle over the meaning of the indictment of I. Lewis "Scooter" Libby, former chief of staff to Vice President Cheney, will be waged by Democrats and Republicans in the media and in the halls of Congress. The legal battle, however, will be waged by prosecutors and defense attorneys just three blocks west of the Capitol, at the E. Barrett Prettyman federal courthouse -- and the rules of engagement will be very different.

Only Special Counsel Patrick J. Fitzgerald's team knows the precise nature and scope of the evidence, but judging from the indictment, convicting Libby in a court of law is going to prove far more difficult than convicting the Bush White House in the court of public opinion.

That has a lot to do with the crimes alleged in the Libby indictment: perjury, making false statements and obstruction of justice. True, as any white-collar criminal defense attorney will tell you, it is often easier to convict someone of lying to investigators than it is to convict a person of committing the offenses that prompted the investigation in the first place. That's because there aren't many technicalities for defense lawyers to use when it comes to the relatively straightforward statutes about making false statements under oath. Indeed, that presumably explains why Fitzgerald, like those who prosecuted Martha Stewart, investment banker Frank Quattrone and the accounting firm Arthur Andersen, chose to pursue an indictment only on charges related to obstructing the investigation, not on the underlying offense. As is often the case, it's not the crime, it's the coverup.

But that hardly means that proving the alleged coverup will be easy.

Two massive hurdles stand in Fitzgerald's way. First, the indictment's 22 pages fundamentally boil down to allegations that Libby lied, both to FBI agents and to the grand jury, about what happened during conversations with two different reporters: one with NBC's Tim Russert on July 10 or 11, 2003, and one with Time's Matthew Cooper on July 12, 2003. In the absence of a tape recording of these private, off-the-record conversations, the prosecutor's hurdle will be to prove beyond a reasonable doubt that the reporters' recollections of these conversations represent what actually happened; in other words, that Libby's testimony was false. This could easily amount to little more than a "he said/she said" swearing contest, and juries justifiably often demand far more from prosecutors before deciding to send someone to prison.

Second, even if Fitzgerald is able to persuade the jurors to accept Russert's and Cooper's recollections of events, the fact that Libby testified falsely does not, by itself, make him guilty of anything. Under the law, Libby cannot be convicted of perjury, making false statements or obstruction of justice unless the prosecutor can persuade the jury beyond a reasonable doubt that Libby knew he was lying at the moment those words left his mouth and that he uttered those words with the intention of deceiving the FBI and the grand jury. It's not nearly enough to prove that Libby got it wrong. Fitzgerald's team must prove that he did it on purpose.

As most of America knows by now, the case centers on Libby's one-on-one conversations with reporters regarding former ambassador Joseph Wilson's trip to Niger in 2002 to investigate claims that Iraq had tried to buy uranium yellowcake and the role, if any, of Wilson's wife, CIA operative Valerie Plame, in getting Wilson that assignment. The famous "16 words" in President Bush's 2003 State of the Union address and the Bush administration's efforts to discredit Wilson for calling those words into question are parts of a long and twisted tale.

The false statements that Fitzgerald has zeroed in on, however, are very narrow and specific. The indictment alleges that Libby lied to FBI agents and the grand jury about several matters: stating that Russert had asked him if he was aware that Wilson's wife worked for the CIA; that Russert had told him that "all the reporters knew it;" and that he was surprised by Russert's statements because, at that time, he did not recall knowing that Plame worked at the CIA. But Libby never discussed Wilson's wife with Russert during this conversation on or about July 10, 2003, according to the indictment. The indictment goes on to allege that Libby lied again to the FBI and the grand jury about his conversation with Cooper. According to Libby's accounts to the FBI and the grand jury, he told Cooper that administration officials were hearing from reporters that Wilson's wife worked for the CIA, and that he did not know if this was true. According to the indictment, all Libby did was to confirm, without qualification, that he had heard that Wilson's wife worked at the CIA.

In the cold black and white of the indictment's printed pages, these statements may look like lies. But in the courtroom, they can be defended as mere mistakes that represented Libby's best "good-faith" recollection at the time.

His attorneys are likely to bolster this defense by arguing that Libby's hectic 18-hour-a-day schedule and focus on scores of issues ranging from the war in Iraq to the U.S. economy would wreak havoc on the memory of any devoted public official trying to recall -- with accuracy -- specific events and conversations that took place months before.

In fact, based on my experience both as a prosecutor and a white-collar criminal defense attorney, it is nearly impossible for any busy corporate executive or public official to complete an interview with FBI agents without getting some fact or another wrong. Memory is a tricky thing, and that's why the boilerplate language trial judges use to advise juries says that "two or more persons witnessing an incident or a transaction may simply see or hear it differently. Innocent misrecollection, like failure of recollection, is not an uncommon human experience." It happens so often, in fact, that prosecutors routinely let such inaccuracies go without challenge.

Under the law, that's not lying. It's "misrecollecting," and it happens every day.

That's not to say that the government should never bring a perjury case or that the Libby indictment is right or wrong. My point is that the burden of proving good faith doesn't rest with Libby. The government must prove beyond a reasonable doubt that his false statements were made knowingly and willfully. Without a "smoking gun" e-mail, or a witness who can testify that Libby confided an intent to mislead investigators, that burden will weigh heavily on the prosecution.

The indictment is devoid of any suggestion that Fitzgerald possesses direct evidence, such as a cooperating co-conspirator, of Libby's willful intent to lie. Rather, the indictment focuses on circumstantial evidence, including references to numerous occasions when Libby asked for, received, and discussed with administration officials and reporters information about Wilson's wife.

Fitzgerald's challenge will be to weave together all his pieces of circumstantial evidence into what I call an "Oh, come on!" argument. He must be able to look directly at the jury and, with a delicate mixture of disgust and bemusement, declare: "Oh, come on! Mr. Libby was all over this thing for weeks. Common sense tells you he didn't forget; he lied."

It may work, but it certainly isn't easy. And Fitzgerald's task is made more difficult by the question of motive. In the absence of direct evidence, motive becomes the glue that binds the circumstantial evidence together. In this case, the common perception is that Libby lied to protect his boss, the vice president.

But the indictment itself undercuts that argument. The story would make sense if Libby had lied to the FBI and the grand jury about the source of his information concerning Wilson's wife to cover up the fact that he heard that information earlier from the vice president. The indictment alleges, however, that at the same time Libby was supposedly lying to the FBI about his conversations with Russert and Cooper, he told the agents "that he had previously learned about Wilson's wife's employment from the Vice President."

Without more, the "Oh, come on!" argument is hardly a slam dunk for the prosecution. Indeed, that is why prosecutors bring so few of these cases, even when the alleged lies are outrageous and high profile. For example, in April 1994, executives from America's major tobacco companies testified under oath before Congress that nicotine was not addictive and that no one had proven that smoking caused cancer.

No one in America believed them. A Justice Department task force labored for years to see if it could prove that the tobacco executives had lied. An abundance of documents demonstrated the addictive and carcinogenic nature of tobacco. But because the executives expressed what they insisted was their personal belief, the Justice Department never brought a perjury indictment. If "Oh, come on!" wouldn't work for a case like that, in which the underlying facts seem so simple, then it's easy to see why in this case -- with all its convoluted machinations -- it will be so hard for that argument to succeed.

The long and short of it is that, no matter how at odds with circumstantial evidence it may seem, an individual's good-faith belief that his statements are true is an effective defense. It could work for Scooter Libby, too.

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Michael Levy heads the white-collar defense practice at the law firm of McKee Nelson in Washington. He served as a federal prosecutor in the District of Columbia from 1995 to 1999.