Two students are suspects in the shooting at a Denver area STEM school that killed one student and wounded eight others.

The suspects were apprehended after allegedly targeting two separate areas of the STEM School Highlands Ranch on Tuesday afternoon. Authorities identified Devon Erickson, 18, as one of the suspected shooters.

Authorities identified a second suspect as a juvenile female, but a public defender clarified that the juvenile prefers to use male pronouns. NBC News is not identifying the underage suspect, who has not yet been charged.

Here's what else we know:

Who are the victims?

One student, 18-year-old Kendrick Castillo, was killed in the shooting.

Castillo, who died at the scene, would have finished his high school career on Friday along with the school's other seniors, Douglas County Sheriff Tony Spurlock said.

"The student was going to graduate and would've been out of school in three days,” the sheriff said.

Castillo is credited with saving lives by diving at a shooter, allowing other students time to flee as he was fatally shot.

Eight other people at the school were shot and hospitalized, Spurlock said. By Wednesday morning, five of those who were injured had been released from hospitals, and three remained in intensive care.

Who are the suspects?

Authorities initially described the suspects as an adult male and a juvenile male, but later said the suspect was female. The sheriff described the suspect is a “small young person,” who investigators thought was a juvenile male “by appearance.”

“The identity wasn’t obvious to us when they were taken into custody,” he said Wednesday.

The suspect’s public defender said that the juvenile prefers to to use male pronouns. NBC News is not identifying the underage suspect, who has not yet been charged.

The adult suspect has been identified as 18-year-old Devon Erickson. Erickson made a brief initial appearance in a Douglas County courthouse on Wednesday, where he only uttered the word "no," responding to the judge asking if he had any questions.

Devon Erickson, a suspect in the shooting at a STEM School in Highlands Ranch, Colorado. via Facebook

The juvenile and Erickson knew each other and would sometimes carpool to school together, Spurlock told NBC News.

Erickson had recently posted a senior photo on his Facebook page, where he listed Pokémon and "The Walking Dead" as interests, along with several pop bands. He had also posted pictures of him acting in "Legally Blonde the Musical" and "Les Misérables" at a local community theater.

On his YouTube page, he had posted videos of him singing, and his bio on Twitter read: "I make music I guess."

The suspect's mother, Stephanie Erickson, 56, told the New York Post on Wednesday that the family needed "a little time right now.”

When asked if she had any idea what would lead her son to carry out a school shooting, she said through tears: "I don’t, no.”

What happened?

The shooters, armed with handguns, entered the K-12 school Tuesday afternoon through the middle school, which has no metal detectors and one contracted armed security officer, Spurlock said.

They were both "able to get deep inside the school" because they were students there, he said.

Officers arrived within two minutes and heard gunfire when they entered the school, but they never exchanged gunfire with the suspects, Spurlock said.

One of the suspects had already been restrained by a security officer, and was apprehended within a minute of deputies arriving at the school, Spurlock said. The other was detained in a hallway four minutes later.

He said at least one student "encountered" a shooter. "We're going to hear about very heroic things that have taken place at the school," he added.

Student Nui Giasolli said on NBC's "Today" that Castillo, the student who was killed, "lunged" at the shooter before getting shot.

"A teenager shouldn't have to be worrying about disarming another teenager with a firearm, we should have to be worrying about if our parents catch us on Instagram or Snapchat or something like that," Giasolli said. "We shouldn't have to be worrying about firearms being brought into our classrooms especially by other teenagers."

Giasolli said that Castillo and other students gave "all of us enough time to get underneath our desks, to get ourselves safe, and to run across the room to escape.”

"I think the fact that a lot of us nowadays have to react first and think later is kind of sick," Giasolli said.

Giasolli's mother, Nyki Giasolli, said she believes Castillo saved her daughter's life.

"If it weren't for Kendrick, I think she'd be gone," Nyki Giasolli said, sobbing.

Brad Bialy, the father of senior Brendan Bialy, told NBC News that his son was one of the students who had tackled and disarmed one of the shooters. The teen plans to join the Marine Corps after graduating, his father said.

They “were brave enough to bring him down so that all of us could escape and all of us could be reunited with our families," Giasolli said. “I can’t thank them enough."

What's next?

Prosecutors will formally file charges on Friday, where a decision on bond will also be made.

Spurlock said both Erickson and the juvenile suspect had cooperated with police.

Investigators expect to spend at least two days processing evidence at the school, the sheriff said. They have also been sifting through the suspects' social media profiles, have seized one of the suspect's cars and have served search warrants to comb through their homes.

About 600 students were in a section of the school directly affected by the shooting, and authorities are working to conduct interviews with some of them.

STEM School Highlands Ranch, which has about 1,850 students, is just eight miles southeast of Columbine High School, the site of the April 20, 1999, mass shooting in which two gunmen murdered 12 fellow students and a teacher before killing themselves.

"If you had suggested to anyone behind me or in this room that within 20 years and 20 miles we would have dealt with Columbine, the Aurora theater, Arapahoe High School, the shooting of Zack Parrish and four other deputies, we would have thought you mad. And yet here we are again,” District Attorney George Brauchler said Wednesday.

"We are a resilient people, but the time for resilience isn't going to be within the first 24 hours of this," Brauchler said. "We're going to mourn. We're going to weep. We're going to take care of those who are down and pick ourselves back up, but who we are is we are a kind, compassionate, caring people."

Coloradans marked the 20th anniversary of the Columbine shooting last month, days after a Florida woman, Sol Pais, sparked a security scare that shut down area schools after authorities said she appeared to have an “infatuation” with the massacre and had purchased a shotgun in the area.

Pais, 18, was found dead of an apparent suicide on April 17, two days after she flew to the area, authorities said.

The shooting at Highlands Ranch came one week after two people were killed and four others injured in a shooting at the University of North Carolina at Charlotte.