New court documents outline a narrative of what the suspects say happened before and during in Highlands Ranch last month. One student, 18-year-old Kendrick Castillo, was killed that day. Eight more were injured.
Two suspects, both students at the school, face a number of charges. The 18-year-old faces 48 counts, including first-degree murder. The 16-year-old, who has also been charged with murder, will likely be tried as an adult.
Many of the details in the probable cause statement, which was filed on May 8 but was just unsealed by a judge earlier this week, reveal what the suspects said about their motivations and mindsets.
The night before the attack, the 18-year-old suspect said that the younger one had messaged him on Snapchat telling him not to go to school the next day, that he was "super suicidal" and that he wanted to get revenge on a lot of people.
In his comments, the 16-year-old explained his thinking. The suspect told investigators that he had been planning the shooting for a few weeks and that "he wanted the kids at school to experience bad things, have to suffer from trauma like he has had to in his life." He was in the process of transitioning from female to male; he said students called him disgusting for trying to be a guy.
The day following the Snapchat message, the suspects went to the older suspect's house. The younger one broke into the gun safe that was in the home, using an ax and then a crowbar.
Throughout the narrative laid out in these court documents, the older suspect often portrayed himself an unwilling participant. He says the younger suspect threatened to kill him several times if he didn't do certain things. Earlier in the day he said he had wanted to call the police but never did. Once they were at the school, he said he was going to go to the office to report the incident but instead, went to the bathroom where he had a panic attack.
His reason for not taking action is unclear. During the interview with investigators, he couldn't articulate why he did not try to stop the incident. Instead, he got frustrated and asked for a lawyer.
Midday, on May 7, the court documents describe how the attack unfolded at the STEM School. Gunshots and yelling filled the air in and around room 107. The 18-year-old suspect was tackled by students.
The younger suspect was detained by an armed security guard. This document also indicates that the guard fired at a Douglas County Sheriff's Deputy who had responded to the scene; those shots missed the officer but wounded a female student.
Little data exists to contextualize this scenario, in part because it is rare.
However, in an FBI analysis of 160 active shooter incidents from 2000 to 2013, five of them ended when armed individuals, like civilians or security guards, exchanged gunfire with the suspects.
In the statement, the 16-year-old suspect explained that he had planned to kill himself after the shooting but did not because he didn't know how to work the safety on one of the guns. The suspect told also investigators that he had been having suicidal and homicidal thoughts since he was 12 years old.
Experts disagree on how strong of a connection there is between mass shooters and mental illness. People with serious mental illness are rarely violent. A few perpetrators of mass shootings have had verified histories of being in psychiatric treatment for serious mental illness. But research does show that individuals who commit mass shootings are often angry, feel aggrieved and have revenge fantasies.
The older suspect is scheduled to be in court again in late September; hearings are scheduled for November. Although the 16-year-old is set to be tried as an adult, his lawyers plan to argue for sending his case back to juvenile court.