GREENSBORO, N.C. (AP) - After weeks of testimony about John Edwards' illicit affair and the money used to cover it up, his defense attorneys opened their case Monday by digging into the details of federal campaign finance law.

Edwards has pleaded not guilty to six criminal counts related to campaign finance violations. He is accused of masterminding a scheme to use nearly $1 million in secret payments from two wealthy donors to help hide his pregnant mistress as he sought the Democratic presidential nomination in 2008.

Defense attorneys are attacking the foundation of the prosecution's argument that the money should be considered an illegal campaign contribution intended to influence the outcome of an election.

But even the federal government was split on that, the defense argues: The Federal Election Commission previously decided that the money was not a campaign contribution. In court Monday, a prosecutor from the Department of Justice called that decision irrelevant to their criminal case and argued against the jury being able to hear about it.

The first witness called by the defense was Lora Haggard, who was in charge of campaign finance compliance for Edwards. In 2008, she was chief financial officer of the John Edwards for President committee.

She testified that the money from heiress Rachel "Bunny" Mellon and campaign finance chairman Fred Baron has still never been reported on the campaign's required disclosure reports, because even after Edwards was charged FEC auditors said it didn't need to be.

She also said Edwards was never involved in formulating, filling out or filing campaign finance reports that were sent to the FEC. In the sixth count of his indictment, Edwards is accused of causing his campaign to file a false report through deceit.

"We never gave him a report to review," Haggard said. "He had no input."

The defense had intended to call former FEC chairman Scott Thomas as their first witness Monday morning, but prosecutors objected to his potential expert testimony on the FEC's decision about the money. U.S. District Court Judge Catherine C. Eagles scheduled a hearing for later in the day over whether to limit Thomas' testimony.

The defense opened its case Monday after the judge refused to dismiss the charges on Friday after 14 days of prosecution testimony.

Prosecutors rested their case Thursday by playing a tape of a 2008 national television interview in which the Democrat repeatedly lied about his extramarital affair and denied fathering his mistress' baby. Earlier testimony from a parade of former aides and advisers also showed an unappealing side of Edwards, casting him as a liar and lousy husband.

The defense has not yet indicted whether Edwards or his mistress, Rielle Hunter, will take the stand.

Before winning a U.S. Senate seat in 1998, Edwards made a fortune as a personal injury lawyer renowned for his ability to sway jurors. But his testimony would expose himself to a likely withering cross-examination about his many past lies and personal failings.

Edwards pollster and friend Harrison Hickman took the witness stand shortly before the lunch recess Monday. Ex-Edwards defense lawyer Wade Smith may also be called Monday afternoon.