The ethics investigation into former U.S. Rep. Paul Broun has now become a criminal case, with a former consultant pleading guilty to lying to investigators about a scheme for taxpayers to help finance Broun’s campaigns.

Brett O’Donnell, a high-profile Republican debate coach from Virginia, faces a maximum of five years in prison on one count of making false statements.

His plea Thursday in U.S. District Court in Macon is the first public indication of a criminal investigation into Broun's office. A congressional ethics investigation closed when the Athens Republican left office in January after losing a primary race for the U.S. Senate.

Broun is described as "Congressman A" and his then-chief of staff David Bowser is described as "Person A" in O'Donnell's guilty plea, but the details of the case match up with an Office of Congressional Ethics investigation that names them both.

In the plea, Bowser is quoted as telling O’Donnell that the Office of Congressional Ethics can go “f—- themselves” and that O’Donnell should falsely maintain that he was a volunteer debate coach for Broun’s campaign.

A U.S. Department of Justice official told Channel 2 Action News that the investigation is ongoing, but it’s unclear whether Broun or Bowser is a target.

“There’s at least one and arguably two other players in this conspiracy,” said Noah Bookbinder, a former federal prosecutor for public integrity cases who is now executive director at Citizens for Responsibility and Ethics in Washington. “It would make sense for (O’Donnell) as kind of a low man on the totem pole, for the government to make an effort to have him come in first, plead guilty, cooperate and help them go after the others.”

It is the first time someone has been charged with lying to the Office of Congressional Ethics, a quasi-independent body that refers cases to the member-run U.S. House Ethics Committee.

Bowser, now the chief of staff for U.S. Rep. Mimi Walters, R-Calif., did not respond to a request for comment. He and Broun both told investigators and said publicly that O’Donnell worked for Broun from 2012 to 2014 as a consultant for $2,500 per month to help sharpen Broun’s communications skills on official matters such as floor speeches, while volunteering for Broun’s 2012 House re-election campaign and 2014 Senate bid.

Official funds for members of Congress are not allowed to go toward campaign activity, though official staff often volunteer on the side for campaigns. Many staffers also are paid by a member's campaign and official accounts, and Broun did this for some staff but not O'Donnell. The debate coach was paid $43,750 from 2012 to 2014 from Broun's taxpayer-funded office account, and he performed similar services for other members of Congress.

"What I did is completely ethical and normal and it's a normal process," Broun told The Atlanta Journal-Constitution in December. "I hired somebody to be a part of my communications team, and they helped me in official capacity as part of our communications team."

O’Donnell gave a similar line to OCE investigators, but he later told criminal prosecutors that he had lied.

According to O’Donnell’s guilty plea, he believed that if he did not help the campaigns, his government work would be terminated, and Bowser indicated that O’Donnell would be paid by the Senate campaign later on. Bowser and Broun denied such an arrangement to the OCE.

Email traffic obtained by investigators also indicates that O’Donnell was hired and paid as a campaign debate coach.

For example, in January 2014, O’Donnell went to Africa to do charity work and was away for the first U.S. Senate race debate. Bowser wrote an email to communications director Christine Hardman (who also now works for Walters), copying O’Donnell: “Since our debate consultant actually abandoned us on our first debate for a bunch of Ethiopians who don’t pay him, I may need to send you to Adel this weekend if you are able to go?”

O'Donnell helped prepare Broun for the debates but was fired in March 2014 after news broke of his work with Broun. According to O'Donnell's plea, Bowser told him then: "Now remember your role with the campaign was as a volunteer," which O'Donnell said was the first time he had been told of his volunteer status.

Broun told OCE investigators that he told O’Donnell repeatedly “you’re volunteering for this” campaign work. Asked by investigators why O’Donnell would write in an email “you hired me to coach the candidate” if he was a mere volunteer, Broun replied “beats me.”

Broun's campaign was perpetually low on money when compared with other GOP rivals, providing a possible incentive to shift costs to taxpayers. Broun finished fifth in the May 2014 Republican primary.

Broun held Georgia’s 10th Congressional District from 2007 until the end of 2014, compiling one of the most conservative voting records in the House and often acting as a foe to GOP leadership. He waged a constant battle to reduce government spending, offering a fusillade of program-slashing amendments to spending bills. His tea party-inspired Senate bid never broke through, but recent appearances at Georgia political events have stoked speculation that he might be pondering another campaign.

O'Donnell was a debate coach for many prominent Republicans over the years, including George W. Bush, John McCain and Mitt Romney. He was also a top strategist for then-U.S. Rep. Michele Bachmann when she ran for president in the 2012 cycle.

His sentencing date has not been set.