Shooting occurred Tuesday at STEM School Highlands Ranch in the US state of Colorado, nine of its students were shot—one fatally—and two fellow students are held as suspects, The New York Times reported.

“We know two individuals walked into the STEM school, got deep inside the school and engaged students in two separate locations,” Sheriff Tony Spurlock of Douglas County said at a news conference.

About five hours after the shooting, the Douglas County Sheriff’s Office released a statement confirming that one of the nine who had been shot, an 18-year-old man, had died.

The sheriff’s office identified one of the suspects as Devon Erickson, 18.

Sheriff Spurlock said the suspects, who were armed with a handgun and other weapons, confronted law enforcement officers when they arrived. He said the suspects, Erickson and one juvenile, were not injured.

The sheriff said the injured students were age 15 or older.

Littleton Adventist Hospital in Colorado said five people were transported there after Tuesday’s shooting. Two are in serious condition while three have been discharged, the hospital said. Sky Ridge Medical Center said two children were transported there and were in stable condition. Children’s Hospital Colorado said one victim had been treated at its south campus and then released.

Douglas County is an affluent area south of Denver with about 350,000 people.