Federal investigators today visited Senate Minority Leader Mitch McConnell's campaign headquarters in Louisville, and campaign staffers handed over information pertinent to the investigation of a leaked tape that revealed the campaign's strategy against potential challenger Ashley Judd, a source connected to the McConnell campaign tells ABC News.

The visit is a sign that the leak is being considered seriously by the FBI, which was alerted to the incident only yesterday. McConnell, R-Ky., has suggested that liberal forces in Kentucky bugged his campaign headquarters and leaked a tape of a strategy session to Mother Jones magazine.

READ MORE: Sen. Mitch McConnell Recorded Plotting Against Ashley Judd

In a radio interview today, campaign manager Jesse Benton told Mike Huckabee that FBI agents were at headquarters for about an hour.

"They tell us that they're running down some leads," Benton said. "For various reasons they need to be very cautious about what they share with me and then what I'm allowed to share on the public side. I can't comment any further, but this is an ongoing criminal investigation."

The McConnell campaign is committed to making sure "this is prosecuted to the full extent of the law," according to Benton, who was among the aides in the room for the session that was captured on tape.

The tape revealed the McConnell campaign's plan to attack Judd as "emotionally unbalanced," and to focus on her religious beliefs. Judd last month announced that she would not seek the Democratic Senate nomination, after several months of publicly flirting with a run.

In the aftermath's of the tape's release, McConnell has attacked the political left for what he called "Nixonian tactics" of bugging his campaign headquarters, though it's still not clear who made the tape and who distributed it. The campaign is already fundraising off of the controversy.

Also today, Benton claimed Mother Jones mistakenly transcribed the speaker at the beginning of the presentation. He said the line, "So I just preface my comments that this reflects the work of a lot of folks: Josh, Jesse, Phil Maxson, a lot of LAs, thank them three times, so this is a compilation of work, all the way through" should instead read, "So I just preface my comments that this reflects the work of a lot of folks: Josh, Jesse, Phil Maxson, a lot of LAs, in their free time, so this is a compilation of work, all the way through."

The distinction is important, because the line Mother Jones reported raised the question of whether McConnell's aides violated campaign law.

READ MORE: Was McConnell's Senate Staff Digging Up Dirt on Ashley Judd?

ABC News reporters listened to the recording several times but could not make a definitive judgment on what was said.