A boy targeted his school in a deadly gun rampage, killing one person and shooting several others in the head before turning the gun on himself.
Witnesses said Jaylen Fryberg walked into the cafeteria at Marysville-Pilchuck High School in Washington state and opened fire methodically without shouting or arguing.
They said he was staring at his victims as he shot them at the school, 30 miles north of Seattle.
As other pupils heard the shots they ran out of the cafeteria and building in a chaotic dash to safety while others were told to stay put inside classrooms.
Marysville police commander Robb Lamoureux said Fryberg died of a self-inflicted wound.
Three of the people who were shot had head wounds and were in a critical condition in hospital.
Another victim, a 14-year-old boy, was listed in a serious condition.
Many students described Fryberg as a happy, popular student, but social media accounts suggested he was struggling with an unidentified problem.
On Wednesday, a posting on his Twitter account read: "It won't last ... It'll never last."
It won't last.... It'll never last....— Jaylen Fryberg (@frybergj) October 23, 2014
On Monday, another tweet said: "I should have listened ... You were right ... The whole time you were right."
I should have listened.... You were right... The whole time you were right...😫😖— Jaylen Fryberg (@frybergj) October 21, 2014
It breaks me... It actually does... I know it seems like I'm sweating it off... But I'm not.. And I never will be able to...😔😫😖— Jaylen Fryberg (@frybergj) October 21, 2014
Alright. You fuckin got me.... That broke me😔😤😫— Jaylen Fryberg (@frybergj) October 21, 2014
Brian Patrick said his daughter, a freshman, was 10 feet from the gunman when the shooting occurred. She ran from the cafeteria and immediately called her mother.
Mr Patrick said his daughter told him: "The guy walked into the cafeteria, pulled out a gun and started shooting. No arguing, no yelling."
Student Alan Perez was eating lunch at a nearby table when he heard the gunshots. "He had a little gun in his hand. I saw the flash from the muzzle," he told KING-TV.
Another student, Austin Taylor, told the station the shooter "was just staring down every one of his victims as he shot them".
Jayden Eugenio, 17, was in the library when a fire alarm went off.
Someone came on the intercom and said shots had been fired and students should stay inside. "I was shaking, you would never believe this would happen in your school," he said.
Outside the school, pupils started streaming out of the building, with some trying to jump a fence to get away, witnesses said.
Cedar Parker, 17, said he was driving away from campus when the shooting happened. He let several students into his car as he heard others yelling for their friends.
A crowd of parents waited in a car park outside a nearby church where they were being reunited with their children. Buses pulled up periodically to drop off students evacuated from the school, with some running to hug their mothers or fathers.
Mr Patrick said after the shooting, his other daughter, a senior at the school, called "hysterical" from her classroom. "I thought: 'God let my kids be safe'," he said.
FBI spokeswoman Ayn Dietrich said the agency was helping police and providing specialists to work with victims and their families.
Marysville-Pilchuck High School has many students from the Tulalip Indian tribe. State senator John McCoy, a tribal member, said the shooting had devastated the community.
"We're all related in one shape or form. We live and work and play together," he said.
Students and parents said Fryberg was a member of a prominent family from the nearby Tulalip Indian tribes and a freshman who played for the high school football team.
He was introduced at a football game as a prince in the 2014 homecoming court, according to a video shot by parent Jim McGauhey.
Shaylee Bass, 15, a second-year student at the school, said Fryberg had recently got into a fight with another boy over a girl. "He was very upset about that," she said.
Dude. She tells me everything. And now. I fucking HATE you! Your no longer my "Brother"!😤😤😤— Jaylen Fryberg (@frybergj) September 19, 2014
"He was not a violent person," she said. "His family is known all around town. He was very well known. That's what makes it so bizarre."