On May 7, 2019, an afternoon movie screening in a darkened classroom at STEM School Highlands Ranch, Colorado, became the setting for one of the most devastating school shootings in the state’s history. Devon Erickson, 18 years old at the time, walked through a classroom door, pulled a Glock handgun from a guitar case, and yelled “nobody move.” What followed killed one student, injured eight others, and sent shockwaves through the suburban Denver community that are still being felt years later.
This is a factual account of what happened, how the courts responded, and why the legacy of that day has less to do with Erickson than with the students who fought back.
Who Is Devon Erickson?
Devon Michael Erickson was 18 years old at the time of the May 7, 2019 shooting at STEM School Highlands Ranch, a K-12 charter school in Douglas County, Colorado, located in the Denver suburb of Highlands Ranch. The school held approximately 1,850 students at the time.
Prior to the shooting, Erickson had reportedly made jokes about school shootings on multiple occasions and had even told people around him “don’t come to school.” On Snapchat, he used the screen name ‘devonkillz.’
His co-perpetrator was Alec McKinney, a transgender boy who was 16 at the time. McKinney said he had been planning the attack for weeks, targeting two students in particular who had bullied and ridiculed him due to his gender identity. McKinney told investigators he “wanted the kids at the school to experience bad things, have to suffer from the trauma like he has had to in his life.”
Defense attorneys argued that Erickson was pressured into participating by McKinney, who testified against Erickson after pleading guilty. Erickson’s lawyers described him as a jazz singer who gave lessons to younger students and someone who fell under the sway of McKinney.
Prosecutors saw it very differently.
What Happened on May 7, 2019
At 1:53 pm, Erickson and McKinney entered the school carrying handguns and other weapons hidden in a guitar case and a backpack. They opened fire in classroom 107, shooting students from two doors located on opposite sides of the room.
The class had been watching The Princess Bride in the dark. Devon Erickson was already in the room and had been sent to the nurse’s office after complaining about feeling sick. McKinney waited outside for him. Erickson came out, returned to class, and then texted McKinney to start the shooting. Erickson picked up his guitar case, walked to one of the classroom doors to seal it, and pulled out the Glock.
When Erickson pulled out the gun and told everyone not to move, 18-year-old Kendrick Castillo lunged at him immediately. His action gave other students enough time to hide and flee the room.
At least three students, 18-year-old seniors Kendrick Castillo, Joshua Jones, and Brendan Bialy, charged at Erickson. They jumped from their desks and slammed the gunman against the wall. Erickson fired off several shots during the struggle. Castillo was killed in the process and was the only student who died. Jones was shot twice with non-life-threatening injuries, and Bialy wrestled the handgun away from Erickson during the fight.
Both Erickson and McKinney said they used cocaine before the shooting. Defence toxicologist Wanda Guidry later testified that Erickson had become such a chronic drug user in the months before the shooting, ingesting cocaine, marijuana and cough syrup nearly daily, that he likely “couldn’t think, concentrate or understand” events around him that day.
The “Victim-Hero” Strategy
One of the more disturbing details that emerged during the trial was the plan prosecutors said the two had devised beforehand.
Prosecutors said Erickson and McKinney concocted a “victim-hero” plan in which McKinney would either kill himself or be killed by Erickson. The shootings stopped when Castillo and two other students charged Erickson, whose gun jammed after he fired four times. A school security guard apprehended McKinney.
Chief Deputy District Attorney George Brauchler told jurors that Erickson agreed to participate in the attack as long as it looked like he was pressured into it and possibly emerged as a hero by killing McKinney. He said their strategy unraveled after Castillo rushed Erickson when he pulled out the gun inside the darkened classroom.
McKinney, who testified against Erickson, said he and Erickson had planned the shooting for weeks and that videos of McKinney berating Erickson were staged so that Erickson could claim he had been forced into the shooting.
Erickson’s defence pushed back hard on this account, arguing he was manipulated into joining the attack by McKinney, a new friend who preyed on him during a family crisis, and describing McKinney as schizophrenic and unreliable. The jury didn’t buy it.
Trial, Conviction, and Sentencing
Erickson’s trial began on May 31, 2021.
A jury found Devon Erickson guilty on all 46 counts on June 15, 2021, including first-degree murder, attempted first-degree murder, conspiracy to commit first-degree murder and supplying a juvenile with a handgun.
The sentencing hearing was an emotional reckoning. Judge Theresa Slade listened to the testimony of at least 20 STEM School parents, students, teachers, and school officials. Parents recounted how their children would have to live with bullets in their bodies, and one teacher said that after two years she still felt “terror” when she experienced flashbacks or heard loud noises.
Jones and Bialy, who were shot while helping Castillo subdue Erickson, didn’t hide their disgust. “He killed Kendrick, and he didn’t care,” Jones said. “I would implore you to put him in jail for as long as you can.” “The defendant is a loser,” Bialy said. “He walked into a classroom, armed, with vulnerable students, and he lost.”
The judge said she didn’t think there was anything she could say to Erickson that would make any difference, and noted he never attempted to explain his actions. “So what you do for the rest of your life in prison, that’s not on me. It’s on you,” Judge Slade said.
On September 17, 2021, Devon Michael Erickson was sentenced to life in prison without parole, plus 1,282 years.
Since Erickson was 18 at the time of the attack, he faced a mandatory life sentence under Colorado law. McKinney, who was 16 at the time and tried as a juvenile, was sentenced to life in prison but could become eligible for parole after about 20 years under a program for juvenile offenders.
Kendrick Castillo: The Only Name That Matters
If there is one story that defines the STEM School shooting, it’s not Devon Erickson’s. It’s Kendrick Castillo’s.
The 18-year-old was watching The Princess Bride in his British literature class when the shooter pulled out a gun. Kendrick immediately lunged at Erickson, giving others precious moments to flee. He was shot in the chest and died. His father John Castillo said: “I know that because of what he did, others are alive.”
John Castillo had actually discussed with his son what to do if he were ever confronted by a gunman. His advice was direct: “You don’t have to be the hero.” But Kendrick rejected that, telling his dad he wouldn’t think twice about acting to save others. “You raised me this way. You raised me to be a good person. That’s what I’m doing.”
Kendrick was an 18-year-old student with three days left of high school and a bright future ahead of him. He was an active member of the school’s FIRST Robotics team.
His legacy has only grown. The former Lucent Boulevard in Highlands Ranch was officially renamed Kendrick Castillo Way in December 2024. In August 2025, a petition to open the cause for canonization of Kendrick Castillo to sainthood in the Catholic Church was submitted by clergy from St. Mark Catholic Church in the Diocese of Colorado Springs, the parish of which Kendrick and his family were members.
The Community’s Long Road After the Shooting
The STEM School shooting didn’t leave neat wounds. Survivors shared accounts of enduring trauma, panic attacks, and recurring nightmares of gunshots, blood, screams and heavily armed SWAT teams rescuing those in hiding inside the school.
Victims’ families were left with physical reminders too. One parent, Nykiah Thomas, described her daughter being shot in the lower body during the attack. The doctor told her daughter the bullet would not be removed because it was too close to her fibular artery.
Judge Slade read the sentences for each of Erickson’s convicted crimes alongside the names of the people who survived his attack. “Each one of these people suffered and survived what you did,” she said.
Erickson’s father, Jim Erickson, offered his family’s remorse. “We pray for these people every day,” he said. “We hope that they can find peace, and we hope that they can find forgiveness, and I know that’s a hard ask.”
FAQ
Where is Devon Erickson now?
Devon Erickson is serving a life sentence in a Colorado state prison without the possibility of parole. His sentence also includes an additional 1,282 years for the 46 counts he was convicted on in June 2021.
What was Devon Erickson’s motive?
Prosecutors established that Erickson was a knowing co-conspirator in the attack. The primary motive behind the shooting, according to court documents, was articulated by co-shooter Alec McKinney, who said he wanted classmates who had repeatedly mocked his gender identity to suffer. Whether Erickson shared that motive or was motivated by something else was never fully explained by Erickson himself, who declined to speak at trial or sentencing.
How many people died in the STEM School shooting?
One person died: 18-year-old Kendrick Castillo, who was killed after rushing at Devon Erickson when he pulled out a gun. Eight other students were injured. Castillo was three days away from graduating high school.
What happened to Alec McKinney?
McKinney pleaded guilty and was sentenced to life in prison in July 2020. As he was 16 at the time of the shooting, he is eligible for parole after approximately 20 years under Colorado’s juvenile offender program.
Who were the students who stopped the STEM School shooting?
Kendrick Castillo, Joshua Jones, and Brendan Bialy all rushed at Devon Erickson in classroom 107. Castillo was killed. Jones was shot twice with non-life-threatening injuries. Bialy managed to wrestle the gun away from Erickson. Colorado Governor Jared Polis called Castillo “a real Colorado hero who died trying to protect others.”
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