Twenty years after the Columbine High School massacre, two pistol-packing students walked into their school just seven miles away on Tuesday and opened fire, killing one teenager and wounding eight others.

Police took into custody two suspects at STEM School Highland Ranch outside Denver, Colorado: 18-year-old Devon Erickson and a younger student whom police said they initially misidentified as a boy but later realized was a girl.

“It was a very confusing situation,” Douglas County Sheriff Tony Spurlock said at an early Wednesday morning press conference. “We originally thought the juvenile was a male by appearance.”

The sheriff said authorities were not releasing any information about a possible motive for the shooting.

Erickson will make a first court appearance Wednesday afternoon.

Spurlock said investigators are still piecing together the chain of events and interviewing witnesses, but they expect to hear “heroic things” about how students and staff prevented more bloodshed.

Kendrick Castillo, 18, lunged towards one assailant when the person entered a classroom, senior Nui Giasolli told the New York Times. Several other students then tackled the shooter, allowing Giasolli and others to escape the classroom.

“They didn’t have to risk their lives to save the 15 of us who were left,” Giasolli said.

Brad Bialy told the Times that his son Brendan, an aspiring Marine, and two classmates had attempted to halt the attack as it began, but one of his friends had been shot in the chest. It is unclear if they are the same students who followed Castillo’s lead.

Castillo was shot three times, according to his father, John Castillo, and succumbed to his injuries.

“I wish he had gone and hid, but that’s not his character,” Castillo told the Denver Post. "His character is about protecting people, helping people.”

Eight students, all over 15, were taken to local hospitals; all but three were released by Wednesday morning.

When officers arrived about two minutes after the alarm went off, one suspect had already been restrained by an armed security officer and the other was quickly apprehended in another area of the school, the sheriff said.

Fernando Montoya told Denver7 News that his boy, age 17, had been shot three times but survived his brush with death. “Thank God he’s fine,” he said. “We are so lucky.”

District Attorney George Brauchler noted that the area his office covers had been the site of two other mass shootings, Columbine and the attack on a movie theater in Aurora. It was, he said, impossible to imagine the community would see another such tragedy. “And yet here we are again,” he said.

Colorado Gov. Jared Polis called it a “vicious act of violence.”

“I can hardly even imagine the horror and the grief the families must be feeling,” he said.

The sheriff stressed that the investigation was in its early stages. The FBI was helping police comb the crime scene, and search warrants were executed at the suspects’ homes.

Denver7 News posted an image of a car being towed from Erickson’s home that had “FUCK SOCIETY” painted on its side. A local reporter also said it had “666” and what looked like a pentagram on the hood. Spurlock declined to comment.

Aiden Beatty said Erickson was his friend, telling the Denver Post the attack “came completely out of nowhere.” Beatty recalled Erickson claiming some students didn’t like him, but that it didn’t sound serious. Erickson’s girlfriend broke up with him several weeks ago, Beatty said.

“In my mind he’s pretty much dead,” Beatty said of his friend. “He’s effectively killed himself, too, in a terrible and unimaginable way.”

Because Erickson and the other suspect were students, they got “deep into the school,” which did not have metal detectors, Spurlock said.

Vivaan Kalura, 12, could hear it from his math class. According to the Denver Post, he texted his mom: “THERE IS A SHOOTING AT SHOOL.”

The first text arrived on Preeti Grover’s phone at 1:59 p.m. Quickly followed by two more:

“IM FING SCARED.”

“TWO KIDS HAVE BEEN SHOT.”

Within eight minutes, Grover said she had raced to the school to discover that Vivaan and his little brother had been evacuated. Vivaan had seen pools of blood staining the corridor as he was led away to safety by police.

One mother said she had received a call from her daughter, who said: “Mommy, there’s a gunshot at my school,” she told KDVR.

Rocco DeChalk, who lives close to the school, saw he saw one of the kids who had been shot in the back. He was sitting by a mailbox on his street.

He’d seen the students sprinting away from the school, but thought at first that it was nothing unusual. “I saw all of them running, so I thought it was a gym class at first,” he told NBC News. “But then I saw there were so many of them.”

He carried the boy into his house after the 911 operator told them to take cover. “He made a comment, ‘Oh, I’m starting to feel it now,’” DeChalk said. “I told him that was probably the adrenaline kicking in and he was going into shock.”