GREENSBORO, N.C. - Andrew Young was once much more than an aide to John Edwards.

The linchpin of the government's criminal case against the former presidential candidate spent long hours driving to and from political events with the rising Democratic star. They attended basketball games together to root for the University of North Carolina and buddied around at Edwards' beach house. Young was even tasked with buying Christmas presents for the Edwards children.

"We were just North Carolina boys and had a lot in common," Young testified Monday. The men were so close that when Edwards got his mistress pregnant in 2007, the married Young publicly claimed paternity of his boss' unborn child.

The former aide was the first witness called by federal prosecutors Monday after opening statements in Edwards' criminal trial, which is being held in Greensboro. Prosecutors allege Edwards masterminded a conspiracy to use nearly $1 million in secret payments from two donors to help hide his pregnant mistress as he sought the White House in 2008.

Edwards, 58, has pleaded not guilty to six criminal counts related to alleged violations of federal campaign-finance laws stemming from accepting money in excess of the $2,300 legal limit for individual contributions. Federal law defines campaign contributions as money given to influence the outcome of a U.S. election.

"It wasn't just a marriage on the line," prosecutor David Harbach said in his opening statement. "If the affair went public it would destroy his chance of becoming president, and he knew it. . . . He made a choice to break the law."

U.S. District Judge Catherine C. Eagles seated 12 jurors and four alternates Monday morning. The panel is made up of nine men and seven women drawn from central North Carolina. Edwards represented the state for one term in the U.S. Senate.

For Edwards and his defense team, destroying Young's credibility is key to their strategy of keeping the former presidential contender out of prison. They allege much of the money at issue in the case was siphoned off by Young and his wife to pay for a $1.5 million house.

"Follow the money," defense lawyer Allison Van Laningham urged jurors in her opening statement. "John Edwards did not get any of this money. Not one cent."

Edwards' lawyers contend the payments were gifts from friends intent on keeping the candidate's wife from finding out about the affair. Elizabeth Edwards died in December 2010 after battling cancer.

A key issue will be whether Edwards knew about the payments made on his behalf by his campaign finance chairman, the late Fred Baron, and campaign donor Rachel "Bunny" Mellon. Each had already given Edwards' campaign the maximum $2,300 individual contribution.

Edwards denies having known about the money, which paid for private jets, hotels, and then-mistress Rielle Hunter's medical care. Prosecutors will seek to prove he sought and directed the payments to cover up his affair, protect his public image as a "family man," and keep his presidential hopes viable.