The 17-year-old who allegedly stabbed a fellow student in a packed Kalani High School math classroom Tuesday knew the victim well.

The two boys were described as longtime friends and swimming teammates.

Police are still investigating what led to the attack, including allegations it was prompted by both boys' interest in a girl.

Yesterday, a petition was filed with Family Court for second-degree attempted murder charges against the 17-year-old suspect. Meanwhile, the 16-year-old victim remains at The Queen's Medical Center, where he was taken in serious condition with stab wounds to his torso.

The stabbing happened about 9 a.m. Tuesday, during the school's first period. The suspect allegedly left the classroom after the stabbing, which happened in front of a teacher and about 30 students, but was detained shortly afterward. He was arrested in the school's office.

Principal Gerald Teramae held a school-wide assembly yesterday to talk about the stabbing, offer counseling services and urge students to "act in a rational manner" in the wake of the incident.

The 30 students who witnessed the attack met with Teramae and other school employees in a separate gathering to ask questions and so that officials could identify students in need of one-on-one counseling.

The stabbing has shocked the school of more than 1,100 students, where acts of violence are rare. It was especially surprising since the victim and suspect often hung out together and were described as longtime friends.

"There was not any previous type of altercation or signs of an altercation. They were friends," Teramae said. "They had gotten along very well. In their social group, they would go out together."

Both boys have been described as good students.

Keith Arakaki, a coach with Hawai'i Swim Club, said he knew the suspect as a good student-athlete and coached the boy up until a few years ago.

"He was doing well in school and swimming," he said.