The only person to die in an attack at a Colorado high school was an 18-year-old who lunged at the two shooters, allowing others to flee.
Kendrick Castillo is said to have leapt from his desk in a literature class and charge at Devon Erickson, 18, and a younger student who has not been named.
The two teenagers are accused of opening fire on fellow students on Tuesday at the Science, Technology, Engineering and Math School in Highlands Ranch, about 25 miles south of Denver.
Mr Castillo’s act allowed others to escape the shooting. Eight students were injured in the attacks.
Witnesses said the teenager, who was due to graduate from the Colorado high school in three days, charged one of the shooters, who killed him.
"Kendrick lunged at him," fellow student Nui Giasolli told NBC News, referring to Erickson, who was being held on Wednesday on murder and attempted-murder charges.
"He shot Kendrick, giving all of us enough time to get underneath our desks, to get ourselves safe, and to run across the room to escape.”
Mr Castillo was described by students as friendly, someone who loved robotics, helping out the elderly in his community and making people laugh.
Cece Bedard said she broke down in tears when she heard her friend had died but was not surprised at his selfless act.
"There is no doubt in my mind that he would have done anything he thought he could have to help anyone," she said.
Mr Castillo’s actions bear similarities with another recent school shooting in the US, in which a student was killed after he challenged a gunman in his classroom.
Rile Howell, 21, was killed during a school shooting at North Carolina at Charlotte last week.
School officials sent out an emergency alert with a matra disseminated by US law enforcement: “Run, hide, fight.”
The three-pronged approach has been endorsed by the US Department of Homeland Security since at least 2012 as part of a public safety campaign, and has been adopted by many workplaces and colleges
