Owen Labrie, 19, in an interview with police, said he and the then 15-year-old girl only kissed and necked in a St. Paul's School building a few days before graduation in 2014, testified Julie Curtin, a detective for Concord, New Hampshire.
Labrie said he put on a condom as "a tease" but, after "a moment of divine inspiration" and self-restraint, sprinted away still wearing the condom, Curtin said.
"He said there was a lot of playfulness and contact back and forth ... and he described a consensual encounter," Curtin testified. "He said their clothes came off but that her underwear never came off. He said that was just a fact."
Later on Tuesday, state criminalist Katie Swango said semen and sperm were found on the young woman's underwear.
Further testing of sperm cells found on the underwear were inconclusive. However, some of the biological material found on the underwear matched Labrie's DNA, she said.
Another state criminalist, Kevin McMahon, said he examined a swab from the accuser's cervix and found no evidence of sperm.
The prosecution rests
The prosecution rested Tuesday. Labrie's lawyers begin their defense on Wednesday. They have indicated Labrie will take the stand in his own defense.
The trial has brought unwanted attention to the elite school
, the alma matter of Secretary of State John Kerry and half a dozen congressmen.
A campus tradition known as the "Senior Salute" has come under fire for allegedly encouraging seniors to have sexual encounters -- ranging from kissing to intercourse -- with as many younger female students as possible.
Curtin said she and another detective initially interviewed Labrie at a coffee shop because that's where he insisted on meeting.
Labrie brought his mother with him, Curtin said, but agreed to move the interview to the police station when he realized she didn't know everything about the Senior Salute tradition.
Labrie first said the girl had the condom, then said it was his, Curtin testified. Labrie called the girl and her sister "angels," the officer said, and insisted he would never have had sex with her because of her age.
When the alleged assault occurred, Labrie was 18 and the girl was 15.
He denied any kind of penetration because she kept her underwear on, Curtin said.
Curtin said Labrie became frustrated because detectives kept asking about the Senior Salute. He said seniors took younger girls' virginity with a sense of pride and that younger girls were often proud to lose their virginity to seniors, Curtin said.
DA says Labrie lured accuser with social media
The young woman testified August 20
and said Labrie penetrated her with his fingers before raping her.
"I was raped!" she said on the stand when a defense lawyer suggested she had sent conflicting signals to the defendant.
On the stand, the girl said she agreed to meet Labrie and accompany him to a machine room. When they kissed, she did not object, she testified. But soon he began to grope her. He bit her chest and tried to remove her underwear, she said.
"I said, 'No, no, no, keep it up here,'" she testified, signaling above her waist. "I tried to be as polite as possible."
Labrie used the Internet and Facebook to entice and lure the girl into a sexual encounter, Deputy Merrimack County Attorney Catherine Ruffle said during her opening statement.
Some of Labrie's friends testified that he told them he had sex with the girl.