He was a high school senior, set to graduate this week.
But instead of celebrating Kendrick Castillo's graduation, the family of the 18-year-old will be mourning his death.
Castillo, a senior at STEM School Highlands Ranch, was killed in a classroom Tuesday in a shooting that police say was carried out by a pair of his classmates: 18-year-old Devon Erickson and a younger classmate who has not been identified because she is a juvenile. Eight other students were injured in the shooting.
The charter school campus has more than 1,800 students in kindergarten through 12th grade, including small children who streamed out of the school weeping and with their arms raised to escape the danger.
Nui Giasolli was in her British literature class when she said a classmate began shooting. She told NBC's "Today" that Castillo lunged at the man who opened fire and was shot. Several other classmates also worked to take the shooter down, she said.
"The next thing I know, he's pulling a gun and telling nobody to move," Giasolli said. "That's when Kendrick lunged at him, and he shot Kendrick, giving us all enough time to get underneath our desks to get ourselves safe, to run across the room to escape."
The shooting happened not far from Columbine High School, a community still on edge after marking the 20th anniversary of a shooting there that shocked the country.
District Attorney George Brauchler, who grew up in the region, said at a news conference Wednesday morning that if someone had told him that in 20 years the region would endure mass shootings, he would have thought them crazy. "These are aberrant acts," he said, despite the fact that several attacks have happened within a 20-mile radius.
Now is the time to mourn and to weep, he said, but the people of Colorado are resilient. "My kids are going to go to school today," he said, acknowledging the conversations anxious parents are having. "I recommend everyone else send their kids, too."
Details of the shooting began to emerge Wednesday.
Within two minutes, the first deputy arrived and confronted a gunman, Douglas County Sheriff Tony Spurlock said. Deputies struggled with the suspects before taking them into custody, he said.
Neither suspect was injured, he said, and no gunfire was exchanged with them. One of the suspects was restrained by the armed private security officer who had been hired to protect the school, Spurlock said.
"I have to believe the quick response of the officers that got inside that school helped save lives," Spurlock said.
About 600 students were in the section of the school where the attack occurred. Authorities are in the early stages of interviewing witnesses and learning what happened, the sheriff said. "We are going to hear about very heroic things that happened at that school."
Five of the students who were shot have been released from hospitals, Spurlock said, and three remain in intensive care.
The wounded students were 15 years old or older, he said. All nine of the students harmed were shot at the school, Spurlock said.
The Denver region has been on edge after the 20th anniversary of the Columbine High School massacre was memorialised, and threats were called in to other Denver-area schools. The Columbine attack, in which two teenagers killed 13 people, marked the beginning of a new era in the United States - a time when the threat of school shootings has taught a generation of children how to flee, hide and even fight back when faced with a shooter.
The week of the anniversary, one of those threats shut down area schools for nearly half a million students when an 18-year-old Florida woman who authorities say was a threat to the community flew to Denver, purchased a weapon and seemingly disappeared. After a two-day manhunt, Sol Pais was found dead of apparent self-inflicted wounds. No one else was injured.
The anniversary came a few days later, and when it was over, the relief was palpable in the community, said John McDonald, head of security for the Jefferson County Public School District.
"But for the school safety community, we can never let our guard down," he said. "This is a reminder of why."
It had been only days since another school shooting. At the University of North Carolina at Charlotte last week, a student tackled a gunman who opened fire in a classroom, police said, killing two and wounding four others.
New York Times: A few pockets of ordinary life bloom in defiance of war.