Raleigh, N.C. — Rielle Hunter, John Edwards' former mistress, went inside the federal courthouse in Raleigh Thursday morning. A grand jury is meeting in the courthouse.

Hunter was taken into a back entrance at the courthouse shortly after 8:30 a.m. by her New Jersey-based lawyer, Michael Critchley, an FBI agent and an agent with the Internal Revenue Service. She was carrying her 18-month-old daughter, Frances.

Hunter left the courthouse about nine hours later without comment.

Edwards, a former U.S. senator from North Carolina and two-time Democratic presidential candidate, is under investigation to see if campaign funds were illegally paid to Hunter, who served as a videographer on Edwards' 2008 presidential campaign.

"When you bring someone before the grand jury, you want to lock in their testimony. I think this is a pretty significant step in the investigation," said Kieran Shanahan, a former federal prosecutor. "Clearly, they are moving along with their investigation if they feel like they need live testimony."

"Some of the questions they'll be asking are how much did you get paid, who did she get that money from and the purposes for any money she received," said Joe Sinsheimer, a Democratic political consultant. "They may well be looking at bank statements and the kind of money she received."

Edwards' political action committee paid Hunter's firm $100,000 for video production in a four-month span in 2006 and then paid an additional $14,086 on April 1, 2007. At the time, the PAC had only $7,932.95 in cash on hand, according to records filed with the Federal Election Commission.

That same day, according to the records, Edwards' presidential campaign paid the PAC $14,034 for what is listed as a "furniture purchase."

The furniture money was one of five contributions to the PAC between April 1 and June 30, 2007. The other four occurred on June 30, the last day of the reporting period, including a $3,000 contribution from the wife of Edwards' finance chairman, Fred Baron.

Baron, a wealthy Dallas-based trial attorney who died of cancer last October, said last year that he quietly began sending money to Hunter to move to California. He said no campaign funds were used and that Hunter was not working for the campaign when he started giving her money.

Edwards has said he was unaware of the payments.

Sinsheimer, who has worked on political corruption cases in the past, said the grand jury is getting down to the nitty-gritty details of the investigation.

"I don't think (Hunter's appearance) tells you anything about the strength of the case, but I do think it tells you they are near the end," he said.

Edwards dropped out of the presidential race in January 2008 after poor showings in early primaries, but he didn't confess to an affair with Hunter until last August.

He has repeatedly denied being the father of her child, saying the affair ended long before the girl was conceived.

The name of the child's father isn't disclosed on her birth certificate, and Hunter has refused to submit her daughter to a paternity test.

"It could be there is a sealed court order requiring Hunter and the baby to submit to DNA analysis. It could be she is voluntarily submitting herself and her baby to DNA analysis,” former federal prosecutor Dan Boyce said while speculating over Hunter's grand jury appearance.

"The fact that a person would be there in the grand jury all day is a very unusual circumstance," he added.

Andrew Young, a long-time Edwards aide, has claimed to be the father of Hunter's child, but he is reportedly writing a book in which he will claim Edwards is the father.

Young showed up at the federal courthouse last month when the grand jury was meeting.