SANTA CLARITA, Calif. >> A 16-year-old boy who killed two students and wounded three others at his Southern California high school before turning a gun on himself died today without investigators discovering the motive for the attack, authorities said.

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 likable, showed no outward signs of violence prior to the attack. After more than 40 interviews, police still don’t know what prompted him to commit such a crime, said Capt. 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 around 7:30 a.m. 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 center 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.

“It wasn’t a spur-of-the-moment act,” Villanueva said.

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.

“We miss her smile, laughter, sweet kisses, and her amazing sense of humor. We will even miss her constant pestering for Starbucks and Cold Stone and anything else with lots of sugar in it. It must have been the reason why she was so sweet.”

Two girls wounded in the attack, ages 14 and 15, were shot in the torso and should be released from the hospital over the weekend, doctors said today. 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 kid 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,” Villanueva said. With this boy, investigators have found “nothing out of the ordinary. He’s a cookie-cutter kid that you could find anywhere.”

In fact, the stereotype of the loser sociopath is often inaccurate, according to the psychologist who co-wrote federal guidelines for assessing school shooting threats and has interviewed five shooters. What pushes most shooters is some kind of loss or disappointment, often recent, followed by the inability to cope with a feeling of being overwhelmed, according to Marisa Randazzo, a former chief research psychologist at the U.S. Secret Service.

“These are acts of suicide as much as homicide,” said Randazzo, who is now CEO of a firm that does threat assessments.

Most shooters she studied were academically successful and weren’t social outcasts.

Friends said while the boy could be introverted, he had a girlfriend and good social network focused on his cross-country teammates.

Randazzo said she expects investigators eventually will learn that someone had an inkling of trouble.

Berhow’s father was an avid hunter who died two years ago. Police said they found several firearms at Berhow’s home and some were unregistered. The Bureau of Alcohol, Tobacco, Firearms and Explosives is working with police to determine where Berhow got the handgun used in the attack.