Devon Erickson Case: Trial, Sentence, and 2024 Appeal

The Devon Erickson case ended with Erickson convicted on all 46 counts tied to the May 7, 2019, shooting at STEM School Highlands Ranch, where he and a co-conspirator killed 18-year-old Kendrick Castillo and wounded eight others. A Douglas County jury returned guilty verdicts on June 15, 2021, and Judge Theresa Michelle Slade sentenced him on September 17, 2021, to mandatory life in prison without the possibility of parole plus an additional 1,200 years.¹² In November 2024, the Colorado Court of Appeals affirmed the judgment in part, vacated it in part, and reversed it in part, remanding the case with directions.³

What Happened at STEM School

STEM School Highlands Ranch is a charter school roughly 15 miles south of Denver. On the morning of the attack, Erickson, then 18, and 16-year-old Alec McKinney left campus during lunch and drove to Erickson’s house. Using an ax and a crowbar, they broke into a parent’s gun safe and took three handguns, a rifle, ammunition, and magazines, hiding the weapons in a guitar case and a backpack before returning to school.⁴

They entered through separate doors, a division that prosecutors said was meant to maximize casualties. Erickson walked into Room 107 with a Glock in the guitar case, magnetically locked the door, drew the gun, and told the students not to move.⁵ Kendrick Castillo, sitting about a foot away, lunged first and shoved Erickson against the wall. Joshua Jones and Brendan Bialy joined the tackle and fought to pry the gun loose.⁶ Jones later testified that he struggled with Erickson for 10 to 15 seconds with the gun pointed at his face.⁷ During the struggle the gun fired four times. Castillo was killed. Jones was shot twice in the leg and survived. Eight students in total were wounded.⁸

Planning and Motive

Police documents and trial testimony placed the origin of the plan in late April 2019, with Erickson and McKinney communicating over Snapchat and Instagram and settling on a shooting at their own school.⁹ McKinney told investigators the two had been planning for a few weeks and had used cocaine together the day of the attack.⁴

Their stated reasons differed. McKinney said he wanted students who had bullied him for being transgender to suffer trauma similar to his own. McKinney testified that Erickson chose Room 107 because it held “the most people he hated” and had once said he “wanted to get away with killing someone.”⁹ Prosecutors described a “victim-hero” plan in which McKinney would die by suicide or be killed by Erickson, letting Erickson present himself as the person who stopped the attack.⁵

The Charges and Trial

Erickson pleaded not guilty and was tried in Douglas County District Court. After delays that pushed the original fall 2020 start, the trial went forward in 2021, with the prosecution calling 61 witnesses and introducing more than 200 exhibits.¹⁰ George Brauchler, the former 18th Judicial District Attorney, stayed on staff specifically to lead the prosecution.¹¹

The Prosecution’s Case

Prosecutors argued Erickson was a willing and calculated participant who acted with “evil in his heart.” Their central witness was McKinney, who had already pleaded guilty. McKinney testified that the attack was Erickson’s idea, that Erickson had a “bucket-list item” to kill someone, and that videos appearing to show McKinney forcing Erickson to use drugs and break into the gun safe were a staged ruse.¹⁰ Brauchler also pushed back on any coercion theory by noting Erickson spent more than 15 minutes away from McKinney before the attack, alerted no adults, and did not press a red panic button while alone in a restroom in the school nurse’s station.⁵

The Defense

Defense attorney David Kaplan did not deny Erickson fired the weapon. He argued Erickson was an unwilling participant under McKinney’s control who lacked the intent to kill, and he urged the jury to consider lesser charges such as second-degree murder or reckless manslaughter.⁸ Toxicologist Wanda Guidry testified that Erickson was a chronic user of cocaine, marijuana, and cough syrup, malnourished and sleep-deprived, and unable to think, concentrate, or understand what was happening. Physiology professor Roger Enoka testified that it was highly likely the gun discharged through involuntary muscle contractions when students rushed Erickson.¹⁰ The prosecution attacked the involuntary-firing theory by pointing to the absence of academic research supporting involuntary contractions producing multiple shots. Erickson did not testify.

The Verdict

On June 15, 2021, the jury convicted Erickson on all 46 counts. The convictions included two counts of first-degree murder (one for deliberated murder and one for murder with extreme indifference), conspiracy to commit first-degree murder, 30 counts of attempted first-degree murder, and 12 additional charges.¹²

The Sentence

Judge Theresa Michelle Slade held the sentencing hearing on September 17, 2021. Victims and family members addressed the court, including Kendrick Castillo’s mother, Maria Castillo, who told the judge her son was her life and her best friend.¹³²

Erickson’s family attended. His father, Jim Erickson, said, “We love Devon unconditionally and we’re so confused how this could have ever happened.” Family members described him as “deeply loving and loved” and said he was not the “monster” he appeared to be, while acknowledging they could not explain his crimes.¹⁴

The 2024 Appeal

Erickson filed a direct appeal. On November 14, 2024, the Colorado Court of Appeals issued an unpublished opinion in case No. 21CA1741, arising from Douglas County District Court No. 19CR451. The three-judge panel, in an opinion by Judge Fox with Judges Johnson and Schock concurring, affirmed the judgment in part, vacated it in part, and reversed it in part, remanding the case with directions.³ Because the opinion is unpublished under Colorado’s appellate rules, the specific grounds for the partial reversal and the instructions on remand are not detailed in the available record. The life-without-parole sentence for first-degree murder was not disturbed on the face of the disposition.

Where the Co-Defendant’s Case Stands

McKinney was charged as an adult but, because he was 16 at the time, could not receive a sentence of life without parole. In February 2020 he pleaded guilty to 17 counts, including first-degree murder, conspiracy to commit first-degree murder, and six counts of attempted murder.¹⁵¹⁶¹⁷¹⁸ None of that applies to Erickson, whose age at the time foreclosed a parole-eligible sentence.

The Castillo Family’s Civil Case

Separate from the criminal case, John and Maria Castillo sued STEM School Highlands Ranch in 2021 under Colorado’s Claire Davis School Safety Act, a 2015 law allowing families to sue schools that fail to exercise reasonable care against foreseeable violence.¹⁹ Under the Colorado Governmental Immunity Act, the maximum recoverable amount was $387,000. The school deposited that sum into the court’s registry without admitting liability, and in February 2023 a Douglas County judge dismissed the case as moot. On November 13, 2025, a three-judge panel of the Colorado Court of Appeals unanimously affirmed the dismissal, holding that the Claire Davis Act does not guarantee a trial when the defendant offers the maximum available damages. The Castillo family planned to seek review in the Colorado Supreme Court.²⁰

1
CNN. Colorado STEM Shooter Sentenced
2
KUNC. Second STEM School Shooter Sentenced to Life in Prison
3
Colorado Judicial Branch. Court of Appeals Opinion, Case No. 21CA1741
4
NBC News. Colorado STEM School Shooting Suspect Targeted Kids Over Gender Taunts
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Denver Post. Devon Erickson Trial, STEM School Shooting
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CBS News Colorado. STEM School Shooting Trial: Brendan Bialy Describes Disarming Devon Erickson
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CBS News Colorado. Devon Erickson, Alec McKinney STEM School Shooting Murder Trial
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Colorado Sun. STEM Shooting Verdict: Devon Erickson Guilty
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Courthouse News Service. Student Sentenced in STEM School Shooting Details Plan at Trial of Co-Conspirator
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Denver Post. STEM Shooting Trial: Defense Rests
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CBS News Colorado. George Brauchler, STEM School Shooting Trial, Devon Erickson
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NBC News. Colorado STEM School Shooter Guilty of 46 Counts Including Murder
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CBS News Colorado. Devon Erickson STEM School Shooting Life Sentence
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Denver Post. Devon Erickson Sentence, STEM School Shooting
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CBS News Colorado. Alec McKinney Sentenced in Deadly STEM School Shooting
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Colorado Sun. Alec McKinney Sentencing, STEM School Shooting
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NBC News. Colorado STEM School Shooter Sentenced to Life, Eligible for Parole
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KDVR. STEM School Shooter Alec McKinney Could Be Released 20 Years Early Under State Program
19
Denver Post. Kendrick Castillo Parents Lawsuit, STEM School Shooting
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Colorado Politics. Appeals Court Rules Civil Trial Over Kendrick Castillo’s Death Not Required if STEM School Pays Max Damages