18 year old, accomplice being held on nearly 30 charges in deadly school shooting

After lunchtime, Devon Erikson allegedly called out "Nobody move" in his class before opening fire, shooting nine and killing one, police said.
3:43 | 05/09/19

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Transcript for 18 year old, accomplice being held on nearly 30 charges in deadly school shooting
But we are going to begin tonight with the horror now revealed inside that school shooting in Colorado. The two suspects, both students, both in court today, and what we have now learned. There was a massive and quick response to the call of an active shooter. Nine students shot, one of them killed, as he rushed the gunman. Children from kindergarten to 12th grade inside that school, their distraught parents waiting for word that they were safe. Tonight, the two young heroes, including that student, Kendrick Castillo who lost his life, what he once told his parents. And the other hero, a young marine recruit. We hear from him right here tonight. ABC's chief national correspondent Matt Gutman leads us off from the scene. Reporter: Tonight, that first glimpse of the young man accused of bringing murder to this Denver area stem school. 18-year-old Devon Erikson, that stripe of fuscia in his hair, nails painted black, saying a single word in his first appearance. No. Reporter: Nodding vigorously when the judge addressed him, but never looking up. He and a 16-year-old accomplice facing near wli 30 charges including murder. Just after lunchtime Tuesday, Erickson allegedly calling out "Nobody move" in his class before opening fire. Nine students shot. One of them killed. His name was Kendrick kas key know. His family saying his son said to them, if there was ever a school shooter, he wouldn't think twice about acting. And tonight, details about his last heroic moments. Complete disregard from his own safety. He was immediately there to respond. He was immediately on the shooter and he was ready to end the threat. Reporter: Brendan bialy was one of the boys who lunged towards the shooter. There was fear. But after that point, it is just doing what I thought I should do. Reporter: These high school seniors, including Castillo, were just three days away from graduation. But there are other heroes as well. As we go through this, I think we're going to find that there were a lot of students that did a number of great heroic things. Reporter: Police there within minutes. They had to force their way into the school and they just happened to pick a door that they forced into that one of the suspects was right, you know, down the hall from that door. Reporter: Soon after the all clear sounded, the kindergarten through high school students bussed to reunification centers, where anxious parents waited and waited for those hugs. Tonight, questions about what allegedly drove that 18-year-old boy and that 16-year-old to murder. We're trying to suspect info. We do have one person shot in the lower back. School's in lockdown. Reporter: The male shooter had been active in school theater. Even had his own YouTube channel featuring cover songs. It didn't seem like he was the type to do it at all. Reporter: But when police searched his house, they found his car spray-painted with "Expletive society." His accomplice, a 16-year-old, also a student at the school. The suspects, the first pair of student shooters to target a school since the columbine massacre 20 years ago. Tonight, that high school changing its sign in solidarity -- "Our hearts are with you, stem." So, let's get live to Matt Gutman in Colorado tonight outside that school, which will remain closed for the rest of the week, we were told, Matt. And we also know the second suspect was also in court today? Reporter: That's right, David. And with a strikingly different demeanor. This suspect, the 16-year-old, had short cropped hair, was engaged and very attentive with the judge and right beside him was sitting his mother, because he is a juvenile. Now, he was born a female, but his defense team petitioned the court that he be recognized as a male. That was granted. The D.A. Is now considering whether or not to charge him as an adult. David? Matt Gutman in Colorado tonight. Matt, thank you.

This transcript has been automatically generated and may not be 100% accurate.

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