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Two crucial witnesses are dead. Another is 100 years old. A fourth was recently held in contempt of court. The daring indictment of two-time presidential candidate John Edwards has pitfalls at every turn for federal prosecutors, adding strain to a Justice Department section still trying to recover after botching its last major political case.

Government attorneys are relying on an untested legal theory to argue that money used to tangentially help a candidate — in this case, by keeping Edwards' pregnant mistress private during his 2008 presidential run — should have been considered a campaign contribution. Edwards' attorneys counter with an argument that's reprehensible but could raise reasonable doubts with a jury: He was only interested in hiding the affair from his cancer-stricken wife, who died in December.

The six-count indictment accuses Edwards of conspiracy, taking illegal campaign contributions and making false statements. On Friday, appearing both defiant and contrite, he insisted he did not break the law.

Some legal experts tend to agree.

At the Citizens for Responsibility and Ethics in Washington, which typically criticizes the Justice Department for not pursuing enough cases against public officials, executive director Melanie Sloan questioned why federal officials were spending resources on this one. She said it is unlikely prosecutors can prove that participants of the scheme intended for the money to aid Edwards' candidacy, and Sloan said it was a stretch to argue that private plane flights provided to mistress Rielle Hunter should somehow be considered campaign contributions.

"This is a really broad definition of campaign contribution," said Sloan, a former federal prosecutor. "It has never been this broadly interpreted."

Sloan predicted a judge will toss the case before it goes to trial.

The federal investigation focused particularly on money coming from two Edwards supporters — former campaign finance chairman Fred Baron and Rachel "Bunny" Mellon, the widow of banking heir Paul Mellon. Combined, they provided $925,000 used to help hide Hunter, according to the indictment.

Prosecutors contend the money was intended to aid his campaign by preventing public disclosure of the affair, which would have destroyed his candidacy. But prosecutors could have difficulty proving intent, given that Baron died in 2008 shortly after the scandal surfaced and Mellon is now 100 years old.

Andrew Young, a former Edwards aide who initially claimed paternity of Hunter's baby and helped keep her in hiding, will likely be a key government witness. Edwards' attorneys have already tried to portray him as being motivated by financial gain.

Hunter sued Young around the time he was releasing a tell-all book, and her attorneys aggressively questioned his credibility. A North Carolina judge said he was troubled by a series of seemingly conflicting statements Young made under oath in the lawsuit involving a purported sex tape depicting Edwards. Superior Court Judge Abraham Penn Jones held Young in contempt and considered sending him to jail before backing away as Young's lawyers argued that the discrepancies were memory lapses.

Young has said he found the sex tape among trash left behind at a home he was renting for Hunter, and he said he held on to the tape to corroborate his story. And if it weren't for Young's book, the plot to conceal Hunter may never have been exposed.

Prosecutors did cite some evidence in their indictment that could be used to argue that participants of the conspiracy knew the money was going to aid Edwards' candidacy. A note from Mellon in 2007 indicated that she wanted to help pay Edwards' bills "without government restrictions."

In another section, prosecutors claim Edwards told a former aide that he was aware of Baron's payments even though he publicly claimed otherwise.

White-collar attorney Matt Miner said although the four counts of receiving illegal campaign contributions may be novel applications of the law, the false statement and conspiracy charges are more straightforward and could be the most problematic for Edwards.

"If Edwards can be shown to have conspired to receive contributions in a way that he would not otherwise have to report — and then those false reports were filed under his signature — both charges are fairly straightforward conspiracy and false statement charges," Miner said.

Still, Tara Malloy, associate legal counsel at The Campaign Legal Center in Washington, said she expects the government to rely heavily on Young's testimony and credibility.

"I don't see an enormous smoking gun for Edwards' involvement," Malloy said.

Edwards initially denied having an affair with Hunter both during his candidacy and after his campaign ended. Baron continued his support of Young and Hunter after the campaign ended as well, adding support to the argument that the money wasn't necessarily related to his candidacy.

In August 2008, Edwards admitted the affair. But he denied fathering Hunter's child until the beginning of last year.

The prosecution is being handled jointly by the U.S. attorney's office in Raleigh and the Justice Department's public integrity section, which is coming off the bungling of its last high-profile case against a public official. Attorneys from the section are under criminal investigation for their handling of the case against the late Sen. Ted Stevens, R-Alaska, whose guilty verdict was vacated after the department admitted it withheld key evidence from the senator's legal team.

Stevens had been convicted of lying on financial disclosure forms about gifts, which ended his political career in 2008. He was killed last year in a plane crash.

Miner said he expects prosecutors were especially careful building their case against Edwards after the Stevens debacle, though Sloan said it could leave the public integrity section with another embarrassing conclusion.

"I think the prosecution is ludicrous," she said.

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Pickler reported from Washington and can be reached at http://twitter.com/nedrapickler. Baker can be reached at http://twitter.com/MikeBakerAP.