On a Tuesday afternoon in May 2019, students in Room 107 at STEM School Highlands Ranch were just trying to relax. It was nearly the end of the year. They were watching The Princess Bride. Then, the world broke.
Devon Erickson and Alec McKinney didn't just walk into that classroom. They stormed it from two different doors, a calculated move designed to trap everyone inside. People often look for a "why" that makes sense. Honestly? In cases like this, the "why" is usually a mess of trauma, anger, and a desperate, dark desire for notoriety.
What followed wasn't just a news headline. It was a tragedy that redefined how we think about school safety, juvenile justice, and the sheer bravery of teenagers who shouldn't have had to be brave.
The Chaos Inside Room 107
It happened fast. 1:53 PM.
Erickson and McKinney had slipped into the school with guns hidden in a guitar case and a backpack. They weren't strangers; they were classmates. They were people the other students saw in the halls every day. When the shooting started, the reaction from the students wasn't just fear—it was action.
Kendrick Castillo didn't hesitate. He was 18, a senior, and by all accounts, a kid who just wanted to help people. He lunged at Erickson. That split-second decision likely saved dozens of lives, but it cost him his. Two other students, Joshua Jones and Brendan Bialy, jumped in too. They managed to submerge the threat, pinning Erickson down even as Jones was shot three times.
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While this was happening, McKinney was active in another part of the room. It was absolute pandemonium. By the time the police arrived, nine people had been shot. One was dead.
The immediate aftermath was a blur of sirens and parents waiting at a nearby recreation center, clutching their phones and praying for a text back.
Who Are Devon Erickson and Alec McKinney?
To understand what happened, you have to look at the two individuals involved, though their backgrounds are vastly different.
Devon Erickson was 18 at the time. In court, his defense tried to paint him as a victim himself—someone pressured by McKinney into participating. They claimed he was "threatened" and didn't actually want to pull the trigger. The jury didn't buy it. Prosecutors pointed to his social media and the way he helped plan the attack as evidence of a willing participant. He was the one who brought the guns from his parents' safe.
Alec McKinney was 16. Born biologically female and identifying as a transgender male, McKinney’s story is deeply colored by a history of trauma. During court proceedings, his mother testified about a home life filled with drug use, domestic violence, and neglect. McKinney told investigators he wanted the other students to "suffer from trauma" like he had. He specifically targeted students who he felt had mocked his transition.
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The dynamic between the two was toxic. They allegedly spent weeks planning the attack, even using Snapchat to coordinate their moves. It wasn't a spur-of-the-moment breakdown. It was a deliberate, cold-blooded plan.
The Long Road Through the Courtroom
Justice in Colorado is complicated, especially when it involves a juvenile and an adult working together.
- The Adult Sentence: Since Devon Erickson was 18, he was tried as an adult. In June 2021, he was convicted of 46 counts, including first-degree murder. The judge didn't hold back. He was sentenced to life in prison without the possibility of parole, plus an additional 1,282.5 years. Basically, he will never walk free again.
- The Juvenile Factor: Alec McKinney was 16, which triggered a massive legal battle. His defense wanted the case moved to juvenile court, where he would have been out in a few years. The judge denied that. However, because he was a minor at the time of the crime, Colorado law (and U.S. Supreme Court precedents) prevents him from being sentenced to life without parole.
- McKinney's Sentence: He pleaded guilty and received a life sentence, but with a catch. He is eligible for parole after 40 years. There’s also a state program for juvenile offenders that could potentially see him released in about 20 to 25 years if he shows significant rehabilitation.
At his sentencing, McKinney actually spoke. He apologized. He told the court he didn't deserve forgiveness. Whether that was genuine or a legal strategy depends on who you ask—Kendrick Castillo’s father, John, has been vocal that he views it as "crocodile tears."
What Most People Get Wrong About the Case
There’s a lot of misinformation floating around the internet about this case, mostly because it involves a transgender shooter and a complex "manipulation" defense.
First off, the idea that Erickson was just a "scared kid" forced into it has been thoroughly debunked by the evidence. He had multiple opportunities to stop the attack or alert someone. He didn't.
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Secondly, people often focus on the private security guard at the school. It’s true that in the chaos, the security guard accidentally fired his weapon, wounding two students. It was a mess. But the primary responsibility, both legally and morally, stayed with Erickson and McKinney.
Why This Still Matters in 2026
The STEM School shooting changed Colorado law. It sparked massive debates about school security—specifically the use of private security versus School Resource Officers (SROs). It also forced a hard look at how schools handle bullying and mental health warnings.
Years later, the community is still healing. Kendrick Castillo’s name is everywhere in Highlands Ranch. There’s a post office named after him. There are scholarships. His parents have become fierce advocates for school safety, ensuring that their son’s bravery isn't forgotten.
Actionable Insights for School Safety
If you're a parent or an educator looking at this case, the "takeaways" aren't just about locked doors.
- Watch the "Leakage": Almost all school shooters "leak" their intentions. In this case, there were social media posts and even a Wikipedia edit that hinted at what was coming. Digital monitoring and taking "jokes" seriously is vital.
- Peer-to-Peer Reporting: Students are the first line of defense. Creating an environment where kids feel safe reporting a friend's disturbing behavior without feeling like a "snitch" is the most effective way to stop an attack before it starts.
- Mental Health Intervention: McKinney’s history was a massive red flag. Trauma-informed care in schools isn't just a "nice to have" anymore; it’s a necessity for identifying kids who are spiraling toward violence.
The tragedy of Devon Erickson and Alec McKinney is a reminder that the "monsters" in these stories are often just broken kids from the neighborhood who made a series of horrific, irreversible choices.
For more information on school safety protocols and supporting victims of school violence, you can visit the National Center for School Safety or the Kendrick Castillo Memorial site to see how the community continues to honor the survivors.