Officials guide students off a bus and into a recreation center where they were reunited with their parents after a shooting at a suburban Denver middle school in Highlands Ranch, Colo., Tuesday. (AP photo)

HIGHLANDS RANCH, Colo. — Two high school students shot and killed a classmate and injured eight others at a charter school in a Colorado community that marked the 20th anniversary of one of the nation’s worst school shootings just weeks ago.

Douglas County sheriff’s officials said Devon Erickson, 18, and a younger student walked into the STEM School Highlands Ranch Tuesday afternoon and opened fire on students in two classrooms, prompting students to run shouting through the halls or to hide out of sight as gunfire echoed through school.

“At the moment no one really knew what was going on so I didn’t know they were bullets,” said seventh-grader Sophia Marks. “I just kind of saw like flashes and we heard bangs.”

Within minutes, deputies at a nearby sheriff’s department substation entered the school and arrested the two suspects after a struggle. Both were students at the school and they were not previously known to authorities, Sheriff Tony Spurlock said.

Josh Dutton, 18, told The Associated Press that he was close friends with Devon Erickson in middle school but hadn’t seen him for four years as he went to a different high school.

On Sunday, he spotted Erickson at a local light rail station and said he was shocked at how much his friend had changed.

Erickson wore all black, a hat and sunglasses, was significantly skinnier and didn’t seem interested in talking. “He said he’d just turned 18 and he owned rifles,” Dutton said.

A message left at a phone number listed for Erickson’s home was not immediately returned.

The shooting took place exactly a week after a gunman killed two students and wounded four at the University of North Carolina-Charlotte. It also comes nearly three weeks after neighboring Littleton marked the grim 20th anniversary of the Columbine school massacre that killed 13 people.

The two schools are separated by about 7 miles in adjacent communities south of Denver.

“Tragically, this community and those surrounding it know all too well these hateful and horrible acts of violence,” White House spokesman Judd Deere said in a statement. President Donald Trump had been briefed on the shooting and was in touch with state and local officials, Deere said.