Concord — A former St. Paul’s School teacher didn’t want investigators to know about his sexual relationship with a student, so the two conspired about what to say under oath, the state Attorney General’s Office has alleged.

David O. Pook, 47, of Warner, N.H., was arrested on Wednesday morning and charged with two counts each of witness tampering and conspiracy to commit perjury.

He is the first person to face criminal charges stemming from the state’s ongoing investigation into the Concord boarding school.

Pook was a humanities teacher at St. Paul’s from 2000 to 2008 before he left under what authorities said were “questionable circumstances.” After leaving St. Paul’s, Pook was hired by the Derryfield School, a private day school in Manchester. Court documents show that a former St. Paul’s rector informed administrators at Derryfield that Pook was on personal leave and had decided not to return, but that, if he had, he would have been hired back.

“The school leadership at the time should never have given Mr. Pook a recommendation and the fact that it did not inform Derryfield of Mr. Pook’s boundary issues was a failure for which we apologize,” current St. Paul’s Rector Michael Hirschfeld said in a statement.

Pook was terminated from St. Paul’s in October 2008 after he violated school rules governing boundaries between faculty and students, court records show. Despite the “boundary issues” that Pook violated while at St. Paul’s, the school said on Wednesday it had “no evidence of a sexual relationship between Mr. Pook and a student.”

The Attorney General’s Office said its ongoing investigation shows otherwise. Testimony before a Merrimack County grand jury late last year provided probable cause that Pook and the former student were “engaged in a physical, sexual relationship” during Pook’s tenure, and that “the relationship continued after Pook left SPS, up to and through the present.”

A grand jury subpoena was served to St. Paul’s in early August for records pertaining to Pook’s employment at the school. The records showed several “troubling” interactions, including examples of times Pook had made female students feel uncomfortable, including when he visited their rooms after nightly check-in, used “crude language” in class and tried to stick his wet finger in students’ ears, investigators wrote.

The contents of emails exchanged between Pook and one St. Paul’s student between February 2008 and October 2008 show an emerging relationship and were identified by investigators as the primary reason for Pook’s termination. Some of those emails were included in the state’s sealed motion to disclose records to Derryfield School last fall and were subject to a protective order, but investigators said Pook shared them with the former St. Paul’s student prior to the grand jury.

The former student testified under oath on Dec. 6 that she had no sexual contact with Pook as a student or at any time since. Further, she said her most recent contact with him had been in summer 2017.

Cellphone records, however, show multiple calls between Pook and his former student in October, November and December of last year.

Pook was called before the grand jury to testify on Dec. 7, but “he did not provide any substantive testimony,” according to the Attorney General’s Office.

In a pleading to stop the state’s disclosure of records to the Derryfield School, Pook wrote he had counseled the student who was ready to disclose that she was gay. However, other witnesses told authorities the former student had only had relationships with men. Investigators said Pook lied “to cover up their romantic and sexual relationship.”

Investigators were granted a warrant to search Pook’s Warner home and his vehicles. They seized laptops, a desktop computer, a cellphone, an iPad and other technology, according to court records.

As of Wednesday morning, Pook was listed on Derryfield School’s website as chairman of the history department and a humanities teacher. Soon after the attorney general’s announcement, his name, photo and accompanying accolades were removed. Telephone calls to officials at the school were not returned, and an email to Pook’s Derryfield School address was returned as undeliverable.

The attorney general’s investigation into St. Paul’s School’s handling of reports of sexual assault and misconduct began in July 2017. Attorney General Gordon MacDonald previously said that the office initially will focus on whether the school endangered the welfare of children or broke a law that prohibits the obstruction of criminal investigations.

In launching the criminal probe, the Attorney General’s Office cited two reports released by St. Paul’s in 2017 on faculty abuse of students spanning decades. Top prosecutors also said they would be looking into more recent reports, including sexual conquest games such as the “Senior Salute.” The game took center stage at the 2015 sexual assault trial of St. Paul’s graduate Owen Labrie, a Tunbridge resident who was convicted of using the internet to lure an underclassman for sex.

Associate Attorney General Jane Young said the state’s investigation is active and ongoing.