Raleigh, N.C. — A recent trip by former presidential candidate John Edwards has raised questions about the investigation surrounding him and how he spent campaign funds.

On Friday, the two-time Democratic candidate flew on a private plane to a farm in Upperville, Va., belonging to Rachel “Bunny” Mellon who was a major campaign supporter.

Edwards was all smiles as he stepped off the plane at Raleigh-Durham International Airport Friday afternoon, but he declined to tell WRAL News where he had been.

The WRAL Investigates team learned, through the flight plan and the tail number of the plane, that he was coming from the property of Mellon, heiress to the Mellon fortune.

She could be a witness in a federal probe looking at whether campaign funds were illegally used to cover up Edwards' affair with Rielle Hunter.

The private jet that Edwards flew on Friday is registered to Oak Springs Farms, the corporate entity that holds Mellon's fortune. The flight plan had the plane landing at Mellon's private airstrip.

Defense attorney and former federal prosecutor Kieran Shanahan said Edwards’ trip raises questions.

“The problem with meeting with witnesses, if even it’s wholly unrelated, is that it can be misconstrued,” Shanahan said. “When you’re under investigation, you’re under a different state. You do have the right to remain silent, but you also have to protect yourself.”

Mellon, a 99-year-old heiress to the fortunes of both 19th-century industrialist Andrew Mellon and the Warner-Lambert pharmaceutical company, was a major political contributor to Edwards in his 2008 presidential campaign. She gave $3.4 million in late 2007 to The Alliance for a New America, a Virginia-based non-profit supporting his candidacy.

Nick Baldick, who ran Alliance for a New America, did not return WRAL’s calls for comment.

Around the same time that Mellon’s money was coming in, Alliance for a New America paid out $2.5 million for “consulting services” to an entity called AFNA, LLC, which could be an acronym for the non-profit itself.

There is an AFNA, LLC, registered in Virginia, but a spokesperson said it had no connection to the Edwards campaign. Investigators are likely looking into whether the Alliance for a New America funneled money from Mellon to cover up Edwards' affair.

Around the time of the money exchanges, Hunter gave birth and Edwards admitted to the affair but publicly denied he was the father. Peace College political science Professor David McLennan said those campaign expenses are the kind that are tough for investigators to track.

“We’ve caught up over the years in terms of laws of disclosure, but we still don’t have the investigative staff to really go through and make sure these things are legitimate expenses,” McLennan said. "It's very difficult because of the volume of material you have to go through."

Added into the mix is a tell-all book from Edwards’ former campaign aide, Andrew Young, which is due out in February. A source shared Young's book proposal. In it, he says he was tasked to get money from Mellon. Young initially claimed to father Hunter's child but later said he was covering for Edwards.

Young and Hunter have both testified before a grand jury at the Federal Courthouse in Raleigh.