Marine Maj. Mark Thompson, accused of having sex with two U.S. Naval Academy students, is photographed in Annapolis, Md. (Nikki Kahn/The Washington Post)

When Marine Maj. Mark Thompson appears in court next month, the former instructor at the U.S. Naval Academy will face what military law experts agree is an unusual charge – lying to a journalist.

Thompson, 46, has long fought to prove that he was unfairly convicted of sexual misconduct with two female midshipmen, and brought his allegations of injustice to The Washington Post. But the Post uncovered evidence that Thompson was dishonest when he testified before an administrative board deciding whether he should be kicked out of the service.

After the revelations were published in March, the military launched a new investigation, and in April accused Thompson of lying to the board, encouraging a friend to lie for him at his 2013 court-martial – and lying to a Post reporter about his accusers.

Thompson, a 19-year Marine Corps veteran who served in Afghanistan, is charged with making a false official statement and conduct unbecoming an officer and a gentleman. He is scheduled to be arraigned in August.

At Thompson’s preliminary hearing this spring, the lead prosecutor acknowledged what he called the “novel” application of the conduct-unbecoming charge to Thompson’s statements to a reporter. Marine Corps prosecutor Maj. Babu Kaza submitted two front-page articles into evidence, and said Thompson used the newspaper to spread lies about the female midshipmen.

Kaza argued that Thompson should be imprisoned for 32 months, fined $200,000 and expelled from the Marines. The prosecution is seeking the audio of the interview that helped lead to the new charges against Thompson.

“Thompson went to the ultimate billboard. He tried to get this story disseminated throughout the world,” Kaza said during the Article 32 hearing, a precursor to a court-martial. “That is conduct unbecoming.”

Military law experts agree that the underlying circumstances of the charge that Thompson lied to a reporter are highly unusual, if not unprecedented. They disagree about whether it is a legitimate course to pursue at Thompson’s court-martial, which has yet to be scheduled.

Military law expert Eugene R. Fidell said the charge involving Thompson’s comments to a reporter should not be pursued. The military can make its case against Thompson without it, he said, and he expressed doubts about the validity of a criminal charge based on false statements to the press.

“If that’s a crime, there are a lot of people in Congress and the government in general who should be brought up on charges,” said Fidell, who teaches at Yale Law School.

Being dishonest or misleading during an interview with a journalist does not usually land a person in jail. But military officers are held to higher personal and professional standards than civilians, and can be punished for failing to meet those expectations.

Rachel E. VanLandingham, a retired Air Force Judge Advocate, said the charge against Thompson is consistent with past prosecutions.

“Intentionally telling lies about other people (the two female cadets) to a newspaper reporter in an attempt to get that reporter to publish those lies certainly, if true, falls below the standards the U.S. military expects of its officers,” VanLandingham, a Southwestern Law School professor, said in an email.

The conduct-unbecoming charge is something of a catch all, legal experts said, that penalizes behavior considered dishonorable or compromising, even if it might not otherwise amount to a crime. The provision in military law, known as Article 133, is meant to ensure the integrity of officers, who are entrusted as leaders.

Military courts have found officers in violation for lying to a landlord about their military assignments in order to get out of a lease and telling another member of the military how to use a catheter to avoid drug detection in a urine test.

The strict standards for officers can apply whether or not an officer is on duty and in uniform. Thompson’s attorneys could argue that the conduct was private – a one-on-one conversation in a non-military setting.

But retired Rear Adm. Christian L. Reismeier, who served as chief judge of the Navy, pointed out that Thompson appeared in uniform in photographs he posed for that accompany The Post stories. The events Thompson discussed at length also occurred during his tenure as a history instructor and concerned two midshipmen, whom he knew through the school’s rifle team.

“He’s picked the most public billboard in the world to drag these girls through the mud in order to clear his name. That’s pretty bad. It’s hard to argue that it’s not dishonorable,” Reismeier said.

Thompson’s attorney Kevin B. McDermott did not return phone calls or email messages seeking comment. He and Thompson declined to participate in the May preliminary hearing at Marine Corps Base Quantico, with McDermott referring to the proceedings as a “show trial.”

Throughout his 2013 court-martial and during subsequent testimony to the administrative board, Thompson disputed allegations that he had sex with two midshipmen after a drunken game of strip poker.

One of the accusers, Sarah Stadler, then 23, said the sex with her was consensual and part of an ongoing relationship. Her 21-year-old classmate alleged that Thompson raped her.

He was acquitted of sexual assault, but convicted of five lesser offenses, including indecent conduct and fraternization.

Text messages discovered after The Post contacted Stadler suggest that she and Thompson were involved in a sexual relationship and that Thompson had misrepresented to the board – and to the newspaper – the last time he saw Stadler before she left Annapolis in 2011.

In January 2016, a Post reporter questioned Thompson about the text messages he exchanged with Stadler. Because the Post generally protects the identities of alleged victims of sexual assault, the name of the woman who accused Thompson of rape has been bleeped from the audio.

During a 45-minute interview in January — previously excerpted and now published in full online — reporter John Woodrow Cox showed Thompson copies of the text messages he uncovered and repeatedly asked Thompson why he had lied about Stadler’s late-night visit to his Annapolis home during her graduation weekend.

“I simply had to,” Thompson said in the recorded interview. “When they were coming after me for 41 years, I can’t begin to say, you know, how terrifying that is.”

If he’d been convicted of the rape charge, he might have faced a sentence that long. During the interview, Thompson continued to maintain that he had not had sex with either woman and offered more explanation for not divulging the text messages.

“If I were to say, acknowledge that I thought they were flirtatious, that moved me on the scale closer towards, well, it was probably a relationship,” he said. “So I avoided anything that looked like it could be unduly familiar or flirtatious.”

When Cox again pressed Thompson on why he’d lied, the Marine asserted that he was “never questioned” about his final encounter with Stadler. The reporter reminded Thompson that he had been asked about it both at the administrative hearing and “multiple times” by The Post.

“I simply wanted to distance myself,” Thompson said, “from anything that would look like there was more familiarity than there was.”