A 16-year-old Colorado student pleaded guilty Friday to first-degree murder and 16 other felonies in a shooting assault that left one of his classmates dead and eight others wounded.
Police say Alec McKinney carried out the attack with 19-year-old Devon Erickson at STEM School Highlands Ranch in Denver last Spring. Kendrick Castillo, a classmate who helped tackle one of the shooters, was killed during the May 7, 2019 shooting.
In December, a judge ruled that McKinney would be prosecuted as an adult.
Erickson is facing the same charges but has pleaded not guilty.
Court documents say that the two students were high on cocaine when they walked into the school, located about 13 miles south of Denver, with a guitar case full of guns.
Investigators say Erickson and McKinney used cocaine at Erickson’s house before hacking into his parents’ gun safe with an ax and crowbar.
McKinney was the mastermind behind the shooting, according to police. The teen, who identifies as male, wanted revenge on classmates who mocked him for his gender identity.
McKinney reportedly told police that he "wanted everyone in that school to suffer and realize that the world is a bad place.”
Erickson told investigators he was afraid of McKinney and made several efforts to stop the attack or limit the carnage, according to court documents released in Douglas County, Colorado.
CONTRIBUTING: The Associated Press
This article originally appeared on USA TODAY: Colorado teen pleads guilty in school shooting