WALNUT CREEK — A teen boy who attacked a schoolmate with a knife on campus was sentenced to five years on a secured youth treatment facility, court records show.

The teen pleaded no contest to kidnapping in connection with the 2023 attack on a ninth grade Northgate High School student. He was originally charged with mayhem and attempted murder, after allegedly slicing a girl’s throat, face and arm while wearing a “scream” mask and lying in wait at a secluded part of the campus, police said at the time.

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The case was prosecuted in juvenile court, but details about its result were made public through an 18-page appellate court decision that upholds the boy’s sentence. The hearing says the boy has autism spectrum disorder and other neurodevelopmental disorders. His name was not publicly released due to his age.

After the attack — which was stopped by campus security — authorities found a “kill list” naming three people at the boy’s home, according to court records. He was 14 at the time. Since then, there has been one incident where staff at juvenile hall found a drawing he’d done of a person covered in blood, holding a knife and smiling. Other than that, he has “done well” in custody, the appellate court decision says.

A judge sentenced him to a baseline five-year stay in a secured treatment facility after his January 2024 guilty plea, court records show. In making the decision, the judge rejected harsher and more lenient alternatives, including correctional facilities and residential treatment homes.

On appeal, the boy urged the appellate justices to reject the sentence and find the superior court “abused its discretion.” But the 3-0 decision finds the county judge’s decision was “supported by the record,” and gives him access to “continued in-person therapy and medication management, and … educational needs.”