RALEIGH, N.C. – 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.

Justice Department 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 interested only 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, he insisted he did not break the law.

Some legal experts agree.

At Citizens for Responsibility and Ethics, a Washington think tank that 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 in the scheme intended for the money to aid Edwards’ candidacy, and Sloan, a former federal prosecutor, said it was a stretch to argue that private plane flights provided to mistress Rielle Hunter should be considered campaign contributions.

She 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 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 fiscal gain.

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

Young has said he found the sex tape among trash left behind at a home he rented 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 that could be used to argue that participants in 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 counts are more straightforward.

“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.