Two students opened fire Tuesday inside a Colorado charter school near Columbine High School, killing one classmate and injuring eight others before being taken into custody, authorities said.

Administrators at STEM School, a K-12 charter in the Denver suburb of Highlands Ranch, reported gunshots fired at 1:53 p.m. Deputies from the Douglas County Sheriff’s Office arrived on the scene two minutes later and engaged two suspects.

We know that two individuals walked into the STEM School, got deep inside the school, and engaged students in two separate locations,” Douglas County Sheriff Tony Spurlock told reporters. “There were a number of students that were shot and injured.”

On Wednesday morning, authorities identified the deceased student as Kendrick Castillo, an 18-year-old senior who was due to graduate this week.

Spurlock said the suspects, identified as Devon Erickson, 18, and Maya McKinney, who goes by the name Alec, were taken into custody without exchanging gunfire with police. Both are students at the STEM School.

“At the time, the individuals we believed were in custody were two males,” Spurlock said Wednesday morning. “It wasn’t until we got to this office that we were able to determine that one of the suspects [the juvenile] was a female.”

One of the shooters was being restrained by a school security officer when sheriff’s deputies arrived. Spurlock said authorities were still investigating a possible motive.

At least one student “encountered” the suspects during the shooting, the sheriff said, not elaborating on the specifics of exactly what the student did.

“We are going to hear about very heroic things that have taken place at the school,” said Spurlock.

Eight victims, ages 15 and older, were being treated in local hospitals. No employees or teachers were injured in the shooting, Spurlock said.

Littleton Adventist Hospital received five patients, a spokesperson confirmed to BuzzFeed News. One patient was in a good condition, while another had their condition downgraded from serious to fair Wednesday. The three others have been discharged from the hospital.

Linda Watson, a spokesperson for Sky Ridge Medical Center in Lone Tree, Colorado, said the hospital was treating two juvenile victims. One remained in stable condition Tuesday night, while the other was discharged. Another victim was treated at Children’s Hospital of Colorado’s South Campus in Highlands Ranch and later released.

“Quite a few shots were fired, and police officers, sheriff’s officers were on scene almost immediately,” Douglas County Undersheriff Holly Nicholson-Kluth told reporters, adding that deputies could still hear gunshots as they arrived at the scene and entered the school.

Spurlock said he believed the deputies’ quick response to the shooting saved lives.

“I want to think that that is something that helped,” he said.

The school does not have a resource police officer assigned to the campus but does have private security, Spurlock said.

He declined to provide additional information about the suspects but said they were not on the Douglas County Sheriff’s Office’s radar. A car with graffiti on it was later removed from the home of one of the suspects.

A motive for the shooting has not been determined, and Spurlock said officials did not have any information about anyone at the school being specifically targeted.