A 16-YEAR-OLD boy who killed two students and wounded three others at his southern California high school before shooting himself died yesterday without investigators discovering the motive for the attack.

Nathaniel Tennosuke Berhow died from a head wound. His mother was present when he died, according to a Los Angeles Sheriff’s Department statement.

Berhow, described by friends as quiet but funny and likeable, showed no outward signs of violence prior to the attack.

After more than 40 interviews, police still do not know what prompted him to commit such a crime, said Captain Kent Wegener of the department’s homicide unit. He said no manifesto, diary or suicide note had been found.

“It still remains a mystery why,” Sheriff Alex Villanueva told a press conference. He said it was “a planned attack, it was deliberate”, but “we don’t have” the details behind it.

Berhow opened fire at about 7.30am on Thursday, his birthday, after being dropped off at Saugus High School in the Los Angeles suburb of Santa Clarita.

Video surveillance showed Berhow walk alone to the centre of a quad, drop his backpack, pull out the gun and start firing, police said.

Villanueva said after opening fire Berhow “cleared a malfunction” with the gun and kept shooting. He counted his rounds, Villanueva said, firing about six shots and using the last bullet on himself. The attack took just 16 seconds.

“As far as we know the actual targets were at random,” the sheriff said.

Villanueva said the conclusion that the attack was planned was based on Berhow bringing the weapon, ably handling it and keeping track of the rounds fired.

Three off-duty law enforcement officers were first on the scene and treated some of the wounded until paramedics arrived.

The dead were identified as 15-year-old Gracie Anne Muehlberger and 14-year-old Dominic Blackwell.

In a statement, Bryan and Cindy Muehlberger said they shared the news of their daughter’s death with “unexplainable brokenness”. They described her as their “Cinderella, the daughter we always dreamed to have,” and said her two brothers were heartbroken.

“She will never get to drive a car, fall in love, build a career, get married, have children and do all the other things everyone takes for granted in this short thing called life,” they said.

Two girls wounded in the attack, aged 14 and 15, were shot in the torso and should be released from the hospital over the weekend, doctors said Friday. A 14-year-old boy was treated and released.

The names of the wounded were not released.

Berhow was described as a quiet and smart child who was a Boy Scout and had previously run track for his school.

“You have the image of a loner, someone who is socially awkward, doesn’t get along, some violent tendencies, dark brooding and online strange postings — stuff like that,” Mr Villanueva said.