Greensboro, North Carolina (CNN) -- A former aide to then-presidential candidate John Edwards testified Tuesday he helped cover up Edwards' affair with a campaign videographer.
The scheme, according to Andrew Young, included him claiming he was the father of Rielle Hunter's child to protect Edwards.
Young is the star government witness against Edwards, who is accused of using hundreds of thousands of dollars from 101-year-old heiress Rachel "Bunny" Mellon and another donor to conceal his affair with Hunter.
The candidate asked him to allow Hunter to move in with his family in North Carolina after newspapers began looking into a possible affair in the campaign, Young testified.
The woman lived with the family three months and expected others to dote on her, Young said.
"She could go shopping at Neiman Marcus, but she couldn't go to grocery store," said Young.
More serious was Young's description of how money was allegedly funneled beginning in late 2007.
Young, the first witness in the trial, said Mellon was an enthusiastic supporter who apologized for not being able to give the campaign more than $1 million.
Mellon made personal checks out to her interior decorator, who would write checks that would end up in the account of Young and his wife, the witness told jurors.
Hunter eventually moved to a gated community and the money was used to pay $2,700 monthly rent and purchases of furniture, television and a BMW, Young said. Hunter also was given a credit card bearing a different name.
Prosecutors say Edwards broke federal law by accepting about $725,000 from Mellon and more than $200,000 from Fred Baron, a now-deceased Texas lawyer who was his finance chairman. The money was used to pay for Hunter's living and medical expenses, travel and accommodations to keep her out of sight while he made his second White House run in 2008, prosecutors say.
Edwards is accused of concealing the money from the public and the Federal Election Commission, which polices political contributions, by filing false and misleading campaign disclosure reports.
Young is testifying for the prosecution under a cooperation agreement with the hope that he won't be prosecuted.
Young, who has not undergone cross-examination, also testified that Edwards made a disparaging comment about his mistress after she called to say she was pregnant.
"She was crying, she was distraught, and she needed to speak with Mr. Edwards immediately," Andrew Young told jurors about his conversation in 2007 with Hunter. "I said, 'Somebody better be pregnant or dying. She said, 'nobody's dying,' " Young recounted.
He said he told Edwards about Hunter's pregnancy. Young quoted Edwards as replying that, " 'She's a crazy slut' and there's a 1-in-3 chance it was his child."
Reporters located a pregnant Hunter at a Cary, North Carolina, grocery story in December 2007 and two men came to his house, Young said.
"They knew about affair between Ms. Hunter and Mr. Edwards and they wanted to ask me about it," said Young.
The cover-up, according to Young, began the next day when he got a call from Edwards.
Edwards proposed that the campaign's account of an affair would be between two staffers -- Hunter and Young, the latter testified.
Eventually, all parties agreed to the plan, with Edwards thanking his aide.
"We had been lying a great deal, but also what he was saying rang true, we believed in the causes," Young said. "I wanted my friend to be president. Being friends with the most powerful person on Earth, there's benefits for you, your family."
Edwards admitted his affair with Hunter in 2008, after his presidential ambitions foundered. In 2010, he admitted that he was the father of Hunter's daughter.
"This affair was a gamble with exceedingly high stakes," prosecutor David Harbach told jurors during Monday's opening statements. "If the affair went public, it would have destroyed any chance to become president, and he knew it. Two of his most enthusiastic supporters happened to be wealthy, and he knew that, too. He made a choice to accept hundreds of thousands of dollars. He made a choice to break the law."
Young also testified Tuesday that Hunter was upset because Edwards wouldn't return her calls.
"If I don't talk to him immediately, this is over. I'm tired of living a lie. I'm going to go public," Hunter said, according to Young.
Edwards indicated that Hunter needed to be kept on an allowance, said Young.
"$5,000 a month was the typical amount, but there were a couple of times where we gave $12,000 a month," said Young.
According to Young, Edwards tried to distance himself from the Mellon money of which he was aware while he was interested in becoming U.S. attorney general in a new Democratic administration.
"He said he couldn't know about any of this in case he had to be sworn in for attorney general," Young said.
Young is the author of "The Politician: An Insider's Account of John Edwards's Pursuit of the Presidency and the Scandal That Brought Him Down," in which he accuses Edwards of using money from his benefactors to maintain his relationship with Hunter.
The defense argues that the money Edwards received from Mellon and Baron was for personal reasons: to protect Edwards' wife, Elizabeth, who was dying of cancer, and his family from public humiliation. Edwards has said his actions were wrong but insisted that they were not illegal.
"This was a fall from grace," defense attorney Allison Van Laningham told jurors. "It was that humiliation he was trying to avoid all along."
Edwards could face up to 30 years in prison if convicted of all six felony and misdemeanor counts against him. Seven of the 16 jurors, four of whom are alternates, are women.
Edwards' lawyers wasted no time attacking Young's credibility, starting with their opening statements Monday. Van Laningham alleged that Young consulted with three other witnesses about testimony after the witness list was released three weeks ago and portrayed him as a greedy staffer who has said Edwards is his ticket to the top.
Van Laningham also pointed out that Young had his own affair, a one-night stand with a campaign employee.
Experts say the government faces an uphill battle to convict Edwards in a legal field riddled with loopholes. The former senator refused a plea bargain to misdemeanor charges that would have given him a few months in prison but would have allowed him to keep his law license.
His wife, Elizabeth, died of cancer in December 2010. The pair had separated after Edwards acknowledged the paternity of Hunter's child, but Edwards was at her bedside when she died.
Jurors also heard voice mails of calls between Edwards and Young.
In one excerpt, the candidate tells Young he should tell his wife about the situation.
And a January 2008 call by Edwards made a reference to Hunter, according to Young:
"Just wanted for all of you, including her, to know that I'm thinking about you."