Laungatasi Ahio turned himself in at South San Francisco police headquarters at about 5:30 p.m. Thursday, Millbrae police Cmdr. Mark Raffaelli said.
Ahio, a Millbrae resident, had been sought by police following the fatal stabbing of 19-year-old Jared Afu at about 11:30 p.m. Wednesday at the school, located at 400 Murchison Drive.
Afu was found by police near the on-campus tennis courts suffering from multiple stab wounds. He was pronounced dead at the scene, Raffaelli said.
Afu and three of his friends had walked to the area of the tennis courts and were smoking cigarettes. Ahio had "a personal issue" with Afu and followed the group to the location where the stabbing occurred, Raffaelli said.
Police were originally seeking two suspects in connection with the homicide, but Raffaelli said today that another man who was with Ahio prior to the stabbing has been identified and is not being treated as a suspect.
"He's probably a person of interest or a witness, but the information we have from other people is that both these individuals walked up, but the second man walked away" prior to the stabbing, Raffaelli said.
Police also located the murder weapon Thursday. It was found several blocks away from the scene of the stabbing and was hidden on a private property, he said.
A person on the property found it and called police, according to Raffaelli.
Although the murder occurred on school property, San Mateo Union High School District spokesman Kirk Black said it was not affecting the school since classes are out for the summer. School is scheduled to resume Aug. 16.