Marine Maj. Mark Thompson has long sought to prove he was falsely convicted of having sex with two female students at the U.S. Naval Academy. (Nikki Kahn/The Washington Post)

Marine Maj. Mark Thompson’s friends warned him to leave his case alone. But he couldn’t, a fellow Marine later told investigators.

The former U.S. Naval Academy teacher was fixated on proving that he had been unfairly convicted in 2013 of having sex with two female midshipmen. So he brought his allegations of injustice to The Washington Post — a decision that led to revelations in the case and serious new charges against Thompson.

“I knew it was stupid. There were people who tried to talk him out of the Post article, but he wouldn’t hear it,” Maj. Michael Pretus told investigators in a recording played Friday at Thompson’s preliminary hearing in Quantico, Va. “He was on an obsession course. You couldn’t get him to talk about anything else.”

Thompson, who has spent 19 years in the Marine Corps, including service in Afghanistan, and taught history at the Naval Academy, now faces charges of making a false official statement and of conduct unbecoming an officer and a gentleman.

A Marine Corps prosecutor, Maj. Babu Kaza, argued Friday that Thompson, 46, should be locked up for nearly three years, fined $200,000 and kicked out of the service for his pattern of deceptions — lying to military authorities after his conviction, encouraging a friend to lie on his behalf at his court-martial and lying to a Post reporter about his accusers.

“His time in the Marine Corps has been a fraud. He’s compromised every core value we hold dear,” Kaza told the preliminary hearing officer, Lt. Col. Adam N. Subervi. “There’s no place for that to be tolerated, no place for that to be accepted.”

The three-hour Article 32 hearing centered on the government’s April interview with Pretus, Thompson’s longtime friend, who has agreed to cooperate with prosecutors as part of an immunity deal. Last month, Pretus, a decorated Iraq combat veteran, was removed from his position as an instructor at the Naval Academy after being implicated in the sexual misconduct scandal.

Pretus — who was a key witness for the defense at Thompson’s 2013 court-martial — acknowledged in his interview with investigators that he had lied on his comrade’s behalf and also admitted to having a sexual threesome with Thompson and one of his accusers during a visit to Annapolis in 2011.

“I made just a terrible error in judgment. . . . I went along with it,” Pretus told investigators, after they asked him to describe the sexual encounter in graphic detail.

On the recording, Pretus said that Thompson had “completely convinced himself he was innocent, and he was going to get vindicated.”

Pretus also told investigators that he was on the phone with Thompson the night that Midshipman Sarah Stadler, then 23, and a 21-year-old classmate had sex with Thompson after a drunken game of strip poker. Stadler described the threesome as consensual and part of an ongoing relationship. But her friend later accused Thompson of raping her — a charge of which he was acquitted. Thompson mentioned to Pretus during their call that Stadler’s friend was drunk and had just thrown up, and that the two women were in the shower.

“You’re playing with fire,” Pretus said he told Thompson.

The statement Pretus made to investigators contradicted what he told the court-martial jury in 2013 and what Thompson said under oath in 2014 to an administrative board considering whether to expel him from the Marines.

Before the court-martial, Pretus said he and Thompson reviewed phone records of their calls to each other to establish a timeline. Thompson made clear to Pretus what his defense would be.

“He didn’t ask me directly to say that the girls weren’t there or had left, but he implied it,” Pretus said.

Pretus’s lengthy interview with investigators in a conference room at the Naval Academy last month sounded at times like a confessional, as if Pretus were almost relieved to answer their questions.

He had not wanted to testify during Thompson’s court-martial but did so out of loyalty, he said. When Thompson insisted on approaching The Post to write about his case, Pretus began to realize that their allegiance was one-sided.

“It’s hard to keep the loyalty — to continue this charade,” Pretus said. “I knew it was only a matter of time” before the truth would burn both of them.

Thompson was not present in the courtroom to hear any of the testimony in the Article 32 hearing. Earlier, he and his defense team walked out after the preliminary hearing officer read him his rights.

Defense attorney Kevin B. McDermott said he objected to the government’s playing Pretus’s interview recording publicly because it had already been reviewed by Subervi.

“We don’t want to participate in something that is going to be nothing more than a show trial,” McDermott said before leaving the courtroom in the basement of Lejeune Hall at the Marine Corps Base Quantico.

McDermott had earlier sought to waive Thompson’s preliminary hearing, but Marine Brig. Gen. Thomas D. Weidley ordered that it proceed.

Once Thompson’s request for a waiver was denied, the hearing officer barred Post reporter John Woodrow Cox from the courtroom, ruling that he could be a potential witness at a court-martial.

Cox’s article about Thompson was entered into evidence during the proceeding, including the evidence that the major had been dishonest when he testified under oath in 2014 to what is known as a Marine board of inquiry. Asked in January of this year why he had lied to authorities, Thompson described the immense pressure he faced after one of the women asserted that he had raped her.

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

The preliminary-hearing officer has 10 days to determine whether there is probable cause to conclude that a crime has been committed and to make recommendations to Weidley, the general, about whether to proceed to a court-martial and on what specific charges.