LAFAYETTE — An explosive device “very similar to a pipe bomb” was found Monday morning by a teacher inside Centaurus High School, forcing the evacuation of the school and the closure of South Boulder Road for several hours.

Lafayette Cmdr. Gene McCausey said the device had a 9-volt battery and could have hurt those in close proximity had it exploded without being removed from the school building by the teacher. The device was detonated by the Boulder County bomb squad.

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are involved with the investigation, officials said, and police are questioning a male Centaurus student who is a “person of interest.”

The teacher, whose name was not immediately known, found the suspicious package inside the school and took it outside, police said. It was removed from the campus by a robot around 11:30 a.m., driven up the road and detonated around 12:30 p.m. in a dirt construction lot near South Boulder Road and Plaza Drive, away from the school.

“It was an explosive device — so that’s pretty serious,” McCausey said. “It’s taken seriously. You can tell by the response.”

Police received early reports of other devices, but they cleared the school after a thorough search that included help from bomb-sniffing dogs found only the one explosive, McCausey said.

The school will be open on a regular schedule Tuesday.

Police responded to the school shortly after 9 a.m. Monday on the initial report of a bomb. Lafayette police Sgt. Peter Voris said the students were evacuated to a field at nearby Ryan Elementary and were later released for the day.

“Especially with what’s happened around the nation recently, we are taking this very seriously,” he said.

Many of the students walking home from the school said they didn’t know what was going on at first.

“We thought it was a fire drill,” said senior Kayla Vellitt. “They didn’t really tell us anything.”

Added her sister Sarie, “We had no idea what was going on.”

Sophomore Anthony Solis said it took him about 10 to 15 minutes to figure out it wasn’t a fire drill and that there was a report of a suspicious device.

“A lot of people were like, ‘It’s a bomb, it’s a bomb,'” he said.

Around 9:30 a.m., the Lafayette Police Department tweeted: “Investigation at Centaurus HS is for suspicious bag. School safely evacuated and S Boulder Road closed for precaution.”

South Boulder Road was closed between Centaur Village Drive and Edessa Drive for several hours.

The Boulder Valley School District sent a note around 11 a.m. to parents and faculty members informing them of the investigation and evacuation. District officials said they waited on the notification to confirm accurate information after receiving conflicting reports about school dismissal plans.

The district sent a second note around 3 p.m., letting parents know that the school building and parking lot would remain closed Monday evening, with no access to the cars in the parking lot. The parking lot was reopened after 9 p.m., with students and staff members allowed to retrieve cars and park as normal today.

An 18-year-old male Centaurus student was arrested after trying to sneak into the parking lot to retrieve his car, police said, but he wasn’t involved in the bomb scare.

Initially, the school was planning to ask students to park at a nearby church and be shuttled to school Tuesday.

Centaurus Principal Rhonda Haniford sent a third note to parents Monday night, letting them know that school counselors will be available to talk to students and staff members.

“I know that today has been a stressful day for each of our families, staff, and our students,” she wrote. “Thank you for your support and cooperation as we work to return operations to normal at Centaurus High School and celebrate the end of an otherwise terrific year at a fine school.”

Anyone with information about the case is asked to call 303-604-8014 or email policetips@cityoflafayette.com.