CONCORD, N.H. — Owen Labrie, a senior at the St. Paul’s School, made up a list of potential girls for his “senior salute” — a school ritual in which older students proposition younger ones for as much intimacy as they can get away with: a kiss, touching, or more.
It was the spring of 2014, and on the list, held up in court by prosecutors on Tuesday, one girl’s name appeared in capital letters. First, prosecutors said, Mr. Labrie wooed her by email. Then, they said, using a key that was shared among students seeking privacy, he took her to a mechanical room on campus. And there, prosecutors said, he raped her.
“This case is about Owen Labrie sexually assaulting a 15-year-old girl,” said Catherine J. Ruffle, the deputy county attorney, during her opening statement at Mr. Labrie’s trial. “It’s about how he thought about this for months. How he made a plan.”
While Mr. Labrie is the one on trial, prosecutors here have also pointed to both the senior salute and to the key, passed down from senior class to senior class, as vital context for the alleged sexual crimes. In court records and in Tuesday’s opening statement, they described an elite boarding school here that was not just an institution of higher learning and prominent alumni, including Secretary of State John Kerry and Cornelius Vanderbilt III, but also a place of secret rites and sexual conquest.
Mr. Labrie and his friends regularly referred to “slaying” girls, prosecutors said. He told the police that he was one of many students trying to beat out his peers by seeing how often he could “score.”
Mr. Labrie, now 19, of Tunbridge, Vt., has pleaded not guilty to 10 counts, including felonious sexual assault. He has denied having sex with his accuser and says their encounter was consensual.
His trial, in a courtroom filled with his family, relatives of his accuser, and a number of teenagers, has brought a harsh spotlight to the traditions of St. Paul’s, a school more accustomed to admiration for its graduates, from hedge fund executives to senators.
The case has already raised uncomfortable questions about the connection between privilege and sexual assault, and between sexual assault in American colleges and in high schools.
According to the Centers for Disease Control and Prevention, almost half of women who have been raped were assaulted before they were 18.
“This is not filtering down from college to high school,” said Elizabeth A. Armstrong, a professor of sociology at University of Michigan. “It’s always been there in high school.”
The administration at St. Paul’s School has said little about the case. “Allegations about our culture are not emblematic of our school or our values, our rules, or the people that represent our student body, alumni, faculty and staff,” said a statement posted Monday to the school’s website. School officials declined requests for further comment.
Mr. Labrie, however, did not appear to be a troubled student. When the alleged rape occurred, on May 30, 2014, he was a senior who had already been accepted at Harvard, where he planned to study theology. He was a prefect too, given extra responsibility for helping younger students.
Prosecutors said he also relished the gamesmanship of the St. Paul’s Senior Salute. According to an affidavit reviewed by The Associated Press, Mr. Labrie told the police that he was “trying to be No. 1 in the sexual scoring at St. Paul’s School.”
His email to the 15-year-old girl who has accused him of rape included hints of romance, his lawyer said, as he asked the girl if she would join him for a “senior salute.”
“I want to invite you to come with me, to climb these hidden steps,” Mr. Labrie wrote, according to his lawyer, J. W. Carney Jr., who read the exchanges during his opening statement on Tuesday.
Taking the stand on Tuesday, the girl seemed to sob as she identified Mr. Labrie in the courtroom. She was initially put off by his advances, she said, but when a mutual friend of theirs urged her to reconsider, she changed her mind about Mr. Labrie.
“Here’s a person who paid special attention to me,” she said. “How nice.”
But prosecutors said she did not want to have sex. When they went to the mechanical room, prosecutors said, Mr. Labrie tried to pull off her underwear. When she resisted, they said, he began to have sex with her.
Mr. Carney said Tuesday that the encounter was consensual and limited. He pointed to the cordial tone of their online exchanges, as when he called her an angel after the encounter and she returned the compliment, to suggest that the accuser changed her story in hindsight, and he urged jurors to pay close attention to those words.
“They had a date, yes, a senior salute, they got together, they kissed, they hugged,” but there was no sexual intercourse, Mr. Carney said.
Prosecutors said the accuser’s underwear had been examined by investigators, who found DNA that may have been Mr. Labrie’s; in one of the online exchanges Mr. Carney read in court, the accuser asked Mr. Labrie if he had worn a condom, and he said he had. Still, Mr. Carney said the evidence would show that although their bodies rubbed together, their underwear was still on and that Mr. Labrie ultimately decided not to have sex with her.
For St. Paul’s and its alumni, the details of the case are embarrassing, however told.
Founded in 1856, St. Paul’s is an Episcopal preparatory school of extreme selectivity, with about 500 students, where tradition runs deep, both officially (twice a week, students dress formally for a so-called Seated Meal) and informally, among students.
Shamus Khan, an alumnus who is now an associate professor of sociology at Columbia University, described the role of ritual at the school in his 2011 book, “Privilege: The Making of an Adolescent Elite at St. Paul’s School.”
He wrote that rituals are used there mainly to impose hierarchy, with some of the rituals organized by students having taken on a pointedly sexual turn. There is the annual dance, called Screw, when “the sexual desirability of girls is determined by their value on the ‘screw’ marketplace,” he wrote. He also described “newb nights,” in which new female students had to divulge their sexual pasts.
“There was the common denominator of sex and sexuality as the pathway to belonging and ‘welcoming’ for girls,” wrote Dr. Khan, who also taught at the school.
During his opening statement, Mr. Carney said the senior salute was a longstanding tradition at the school, which began admitting female students in 1971, in which some of the young women willingly took part.
“The girls would be honored and proud about this, that they were the focus of the senior salute,” Mr. Carney said.
But here in Concord and at other elite boarding schools in the region, the allegations in Mr. Labrie’s case have led to outrage and anguished questions about how what began as a school ritual may have become an excuse for sexual assault.
“Have the lines blurred between federal crimes against our fellow peers and tradition?” wrote a group of students at Phillips Exeter Academy, another elite prep school, in their school paper, after Mr. Labrie was charged last year.
“People are pretty shocked that it happened in such a quaint part of town, and the nicest part of town,” said Lindsey Luker, 22, a recent college graduate, who grew up here. “It tainted the picture-perfect St. Paul’s.”
Jess Bidgood reported from Concord, and Motoko Rich from New York.
By JESS BIDGOOD and MOTOKO RICH