A 15-year-old boy is in custody in Colorado, accused of stabbing a 19-year-old woman to death—and police say he planned to keep killing. The suspect, whose name has not been released, was arrested early Sunday, hours after Makayla Grote—a racetrack employee and aspiring NASCAR driver, notes KDVR—was fatally stabbed at her apartment in Longmont, CBS Denver reports. Per court documents, the teen exchanged "troubling text messages" weeks ago with Grote's younger sister that she reported to police. He allegedly attacked Makayla with a hunting knife when he arrived at the apartment around 6:15pm and she opened the door. Police say her younger sister locked herself in a bedroom and the teen left after he was unable to get inside.
Investigators say they found a "death list" in the suspect's bedroom, the Longmont Times-Call reports. Makayla's sister was at the top of the list, though his notes said that he would kill anybody who got in the way, Deputy DA Michael Foote says. When he was arrested, he was driving his parents' vehicle and was about a mile away from the third name on the list, per Foote. He adds that the day before the stabbing, the teen assaulted his grandfather and threatened his mother with a knife. He was reported as a runaway the same day. Prosecutors are considering charging the teen as an adult. He's being held without bond and was due in court Monday, though he chose to skip the appearance after being told he would be held in restraints. (Read more murder stories.)