One student was killed in the May 2019 shooting at STEM School Highlands Ranch.

A 16-year-old accused in a Colorado school shooting pleaded guilty to multiple charges, including murder, on Friday.

Two teenagers, Alec McKinney and Devon Erickson, were arrested after allegedly opening fire at the STEM School Highlands Ranch near Denver on May 7, 2019.

Kendrick Castillo, an 18-year-old who tried to confront the shooters, was killed. Multiple students were injured.

McKinney — who was born biologically female but identifies as male — pleaded guilty Friday to multiple charges, including first-degree murder, attempted murder and conspiracy to commit first-degree murder after deliberation.

The mandatory minimum sentence is life with the possibility of parole after 40 years minus earned time, prosecutors said.

McKinney’s sentencing is set for May 18, prosecutors said.

Erickson, 18, pleaded not guilty. He has a trial scheduled for May, The Denver Post reported.