One student died and eight classmates were wounded Tuesday in a shooting at a suburban Denver school, law enforcement authorities said — a shooting that happened less than a month after the region marked the 20th anniversary of the Columbine massacre.

The student who died was a senior who was expected to graduate in just three days, officials said. He died at the school.

Two suspects, both students at the school, are in custody, according to Douglas County officials. The adult suspect was named late Tuesday as Devon Erickson, 18. The other suspect is a juvenile female, “a small, young person,” Douglas County Sheriff Tony Spurlock said.

The Denver region has been on edge as the 20th anniversary of the Columbine High School massacre was memorialized, and deadly threats were called in to other Denver-area schools. The Columbine attack, in which two teenagers killed 13 people, marked the beginning of a new era in the United States — a time when the threat of school shootings has taught a generation of children how to flee, hide and even fight back when faced with a gunman.

“This is not who we are,” District Attorney George Brauchler said at a news conference Wednesday morning, adding that he had grown up in the area and that if someone had told him that in 20 years the region would endure multiple mass shootings, he would have thought them crazy. “These are aberrant acts,” he said, despite the fact that several attacks have happened within a 20-mile radius.

Now is the time to mourn and to weep, he said, but the people of Colorado are resilient. “My kids are going to go to school today,” he said, acknowledging the conversations anxious parents are having. “I recommend everyone else send their kids, too.”

The week of the anniversary, one of those threats shut down area schools for nearly half a million students when an 18-year-old Florida woman who authorities say was a threat to the community flew to Denver, purchased a weapon and seemingly disappeared. After a two-day manhunt, Sol Pais was found dead of apparent self-inflicted wounds. No one else was injured.

The anniversary came a few days later, and when it was over, the relief was palpable in the community, said John McDonald, head of security for the Jefferson County Public School District.

“But for the school safety community, we can never let our guard down,” he said. “This is a reminder of why.”

It had been only days since another school shooting. At the University of North Carolina at Charlotte last week, a student tackled a gunman who opened fire in a classroom, police said, killing two and wounding four others.

The Colorado shooting happened shortly before 2 p.m. Tuesday local time at the STEM School Highlands Ranch — a charter school campus with more than 1,800 students in kindergarten through 12th grade.

The shooters were able to walk in through a middle-school entrance that does not have a metal detector and get deep inside the school, Spurlock said.

Two pistols were used in the shooting, Spurlock said, but he declined to give further information about the weapons at a Wednesday morning news conference. Neither suspect would have been legally able to purchase a gun, Spurlock said.

Holly Nicholson-Kluth, undersheriff for the Douglas County Sheriff’s Office, said the shooting started in the middle-school portion of the campus, and an administrator called police after hearing shots.

“Quite a few” shots were fired, Nicholson-Kluth said.

She said her agency has a substation blocks from the school and responded quickly.

Officers could hear gunshots as they arrived, she said.

Within two minutes, the first deputy arrived and confronted a gunman, Spurlock said. Deputies struggled with the suspects before taking them into custody, he said.

Neither suspect was injured, he said, and no gunfire was exchanged with them. One of the suspects was restrained by the armed private security officer who had been hired to protect the school, Spurlock said.

“I have to believe the quick response of the officers that got inside that school helped save lives,” Spurlock said.

With so many students, about 600 were in the section of the school where the attack unfolded, authorities are still in the early stages of interviewing witnesses and learning what happened, he said. “We are going to hear about very heroic things that happened at that school.”

Five of the students who were shot have been released from hospitals, Spurlock said, and three remain in intensive care.

The wounded students were 15 years old or older, he said. All nine of the students harmed were shot at the school, Spurlock said.

Douglas County Coroner Jill Romann has not identified the student who was killed, according to the sheriff’s department, but confirmed that the victim is an 18-year-old male.

The suspects were “not on the radar” of law enforcement, as far as he knew, he said.

Spurlock said it was too early to discuss possible motives for the attack. He said a suspect’s car had been seized and searched at the school parking lot, but declined to discuss graffiti on the car, what it might mean or where it came from.

McDonald wondered if there was a chance the attack could have been inspired by the Columbine massacre. During the 1999 attack, two senior boys with explosives and guns killed 13 people inside their school before killing themselves. In the two decades since, the two shooters have become icons in certain corners of the Internet and have inspired dozens of other attacks, including the shootings at Virginia Tech and Sandy Hook Elementary School.

“The fact that there are two suspects, we’ve got to start wondering: What were they studying? Where did this idea come from?” McDonald said.

“This just devastates the whole community. Again. It traumatizes a whole new generation of students,” McDonald said. “People are exhausted. They are tired of this. They are getting mad. Every emotion you can imagine is being felt, and over the course of the coming days, it will be magnified.”

The FBI is investigating the crime scene, Spurlock said, and will be for a couple more days at least.

No teachers or staff members were wounded to his knowledge, Spurlock said.

School officials did not immediately respond to requests for comment Tuesday, but early Wednesday they posted on social media that the school would be closed for the rest of the week and a crisis support center would open to all students, parents and staff.

“It is with unspeakable grief and shocking disbelief that we share this message with our school community,” the statement said. “It is important during this difficult time that our community comes together and that we take care of one another …

“Our thoughts are with everyone who has been impacted by today’s tragedy, and we are heartened by the bravery of our students, staff, parents and first responders.”

Colorado state leaders offered prayers and aid to law enforcement.

Gov. Jared Polis (D) said Wednesday morning that Colorado has been no stranger to tragedy. Just weeks ago, he joined survivors of Columbine, many of whom now have children of their own, for a memorial and a day of service. In this tragedy as well, people will come together to support all of those who were hurt, he said. “We are a resilient state.”

And, he said, “America has seen too many of these senseless acts of violence.”

Perry Stein contributed to this report.