Castillo, 18, was a four-year member of the robotics team and would have finished his senior year in three days.

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The student who died in the shooting at a Colorado charter school on Tuesday was an 18-year-old senior who was due to finish school in just three days, authorities said. Kendrick Castillo was the sole student to die after the shooting at STEM School in Highlands Ranch, Douglas County Sheriff Tony Spurlock told reporters Wednesday. Eight others were injured.

A classmate who witnessed the attack told NBC's Today show that Castillo "lunged" at one of the shooters to save others.

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Nui Giasolli described the shooting that happened inside her British literature class — and how Castillo lost his life protecting his fellow students. "The next thing I know is [the shooter] is pulling a gun and he’s telling nobody to move, and that’s when Kendrick lunged at him," Giasolli said on Today. "And 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." On Twitter, Colorado Gov. Jared Polis shared a local news story citing Giasolli's comments to Today. "Colorado will always remember the heroism of Kendrick Castillo," he wrote. At the Wednesday press conference, Sheriff Spurlock didn't name the students who reportedly tackled the shooters, but said "we are going to hear about very heroic things that have taken place at the school." "I suspect as the detectives get further interviews from them, we’re going to find that there were much more heroic things," Spurlock said. Castillo was an award-winning, four-year member of the school's robotics team. He had already held multiple technology internships, according to his LinkedIn page. On social media, people mourned the loss of Castillo and called him a hero.

This is Kendrick Castillo. Today during the shooting at STEM Highlands Ranch, he tackled one of the shooters and was shot. He went to the hospital where he tragically passed away. He saved the lives of many other students. He deserves to be remembered as a hero. Know his name.

This is 18-year-old Kendrick Castillo. He was the young man killed in the #STEMshooting yesterday. We’re told he was passionate about technology, on the school’s robotics team, and set to graduate in just 3 days. Sending his family so much love during this time. 🙏🏽 @CBSDenver

In the Today interview, Giasolli also thanked "Brendan Bialy, Jackson Gregory, and Lucas Albertoni [for being] some of the kids that were brave enough to bring [the shooter] down so that all of us could escape and all of us could be reunited with our families." "They were very heroic," she said. "I can’t thank them enough." Bialy, whose father told NBC he's planning to become a Marine, reportedly helped to tackle one of the shooters. He was not shot but is "still in shock and primarily concerned with the victims and their families," according to a statement from the family's attorney that was shared with 9News.

Brendan Bialy and other students rushed at the gunman at STEM School Highlands Ranch in Colorado. One of the students was shot in the chest. Police say one student died and 7 others were wounded. Two suspects are in custody: https://t.co/LNasaZ02zM #STEMSchoolShooting