USA TODAY

Published 2:48 PM EDT May 15, 2019

CASTLE ROCK, Colo. — A 16-year-old suspect in last week's deadly shooting rampage at a suburban Denver high school will be tried as an adult on first-degree murder charges, prosecutors said Wednesday.

Alec McKinney, 16, and Devon Erickson, 18, have been jailed since the May 7 assault at the Stem School Highlands Ranch that left one student dead and eight wounded. District Attorney George Brauchler had not revealed until Wednesday whether McKinney would be charged as an adult or a juvenile.

Both suspects had court hearings Wednesday, and court documents briefly made available revealed that both face a long list of charges including murder and attempted murder. Judge Theresa Slade later ordered the documents be sealed after defense attorneys asked that the charges be kept secret for at least another two weeks while they investigate the case. They argued that releasing the charges could sway witness testimony. 

“There are times when it is appropriate to suppress information," Slade said. 

During the two hearings, each defendant sat quietly, wrists and ankles shackled. Erickson, his black hair dyed with purple-pink streaks, didn’t speak or interact with anyone. McKinney spoke only once, in a clear, high voice, to acknowledge a question from the judge. McKinney's attorneys plan to ask Slade to return his case to juvenile court.

Investigators have declined to discuss how the students obtained the weapons. The attack horrified this suburban community where the STEM School is a charter school to which students must request admission.

More: Memorial service Wednesday for teen hero Kendrick Castillo from Denver school shooting

Wednesday's hearing took place hours before services are held for the lone fatality, Kendrick Castillo, a senior at STEM School Highlands Ranch. 

Castillo's parents attended the morning court session. Reporters were kept segregated from family members of the victims and the suspects. 

“I can’t imagine going through a more difficult situation than they are going through,” Brauchler said of the Castillo family. 

The shootings rocked the community and the school. Parents say the charter school, which is technology focused, works hard to create an environment of personal accountability and problem-solving. Bullying isn't tolerated, said parent Candace Craig, who has three kids at the school – if anything, she said, peer pressure shuts down bullying immediately.

Craig said she believes it's important to understand why the attack occurred.

Students accused in shooting face judge

“I want to call them names and reduce them to their actions, but when it’s this close to home, there’s a piece of me that can’t reduce them to what they did,” she said. “We need to hear from them, but I don’t know how that looks in a healthy way.”

The attack unfolded nearly three weeks after neighboring Littleton marked the anniversary of the Columbine attack that killed 13 people. The two schools are separated by about 7 miles in adjacent communities south of Denver.

The local Knights of Columbus, where Castillo often volunteered with his father, was helping pay funeral expenses and providing an honor guard. A procession of hundreds of Jeeps -- a favored vehicle of Castillos -- began the ceremonies.

More: Kendrick Castillo, hero killed in Colo. school shooting, told his dad he would act if confronted with a gunman

Friends remember Castillo as funny, smart and modest and expressed no surprise that he protected his classmates. Castillo, a member of the school’s robotics club who loved to tinker with his own projects, was set to graduate days after he was killed.

Witnesses said Castillo was among three students who tackled a classmate who opened fire in his classroom.

Joshua Jones, who fought back alongside Castillo and Brendan Bialy, was shot twice in the leg. He spoke publicly about the tragedy and Castillo's heroism for the first time Tuesday.

“There wasn’t a whole lot that was going through my mind at the time," he said at a news conference. "Adrenaline and tunnel vision are a crazy thing."

Jones, also an 18-year-old senior, said he called his mother even before authorities arrived at the chaotic scene. Jones described the call: "It was something like 'Hey, mom, there’s been a school shooting. I’ve been involved. The authorities are on the way. They’re going to get an ambulance and I’m going to go to the hospital. That’s all I got right now for you.’”

He said he remains in a "funk" emotionally but that his physical wounds were healing well. And he said the carnage would have been worse if all three had not worked together.

"If it was just me or just Brendan or just Kendrick it would have been much worse for everybody in that room," Jones said.

Details about the armed school security guard who subdued the second suspect also emerged this week. The man’s employer, Boss High Level Protection, was contracted to guard the school that about 1,800 students attend.

The guard, whose name has not been released, fired his weapon inside the school during the response to the shooting, a law enforcement official with knowledge of the case told The Associated Press on Thursday. Two news organizations citing anonymous sources reported that authorities are investigating whether the guard mistakenly fired at a responding sheriff’s deputy and may have wounded a student.

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Brauchler on Wednesday announced he’s asked an outside prosecutor to investigate the security guard's actions, but declined to address specifics: “Given the information that we’ve uncovered, it’s fairest to the process, fairest to the case and fairest to him to have the 4th Judicial District Attorney weigh in.”

The guard’s boss calls him a hero who helped stop the shooting by disarming and detaining one of the shooters.

Bacon reported from McLean, Va. Contributing: The Associated Press