The call — which warned of a shooter at Boulder High School — came via the University of Colorado Boulder’s non-emergency dispatch line at 8:33 a.m. on Wednesday.

What sounded like a male person relayed he was in front of Boulder High School with semi-automatic weapons and that he was prepared to go inside.

Boulder Police Chief Maris Herold, who listened to the call, said that, shortly afterward, there were “active shooting very realistic gun sounds in the background.”

It sounded realistic and “very scary,” Herold said.

None of it actually occurred.

Boulder High School was one of several schools across Colorado that received threats of active shooters, prompting lockdowns, evacuations and shelter-in-place orders. All were later proven hoaxes in a disturbing trend called “swatting.”

Such calls — reporting fake school shootings or other crimes — drain resources from the police, create fear and, in some instances, even result in violence.

Schools in Alamosa, Aspen, Boulder, Brighton, Cañon City, Clear Creek County, Durango, Englewood, Estes Park, Fort Morgan, Gilpin County, Littleton, Glenwood Springs and Carbondale were also effected.

It appeared as if the caller — or callers — were running down a school list in alphabetical order.

Colorado isn’t t the only state that faced swatting calls this week. The fake reports also shut down schools in Idaho and compelled authorities to place an Illinois high school under a “shelter in place” order.

The FBI in Denver said it is aware of the situation.

“FBI Denver is aware of numerous threats made today to a variety of organizations and institutions across Colorado,” the agency said. “The FBI works closely with its law enforcement partners by providing resources and guidance in these investigations and can recommend cases for federal prosecution.

The Colorado Division of Homeland Security and Emergency Management said it is also monitoring the incidents.

The fake calls came on the heels of a school shooting near Denver’s East High School last week, prompting students Tuesday to urge Denver City Council members to restore school resource officers to Denver Public Schools, which ended its contract with the Denver Police Department in June 2020.

In the case of Boulder High School, the police Police ordered residents and businesses in the area to shelter in place after an unconfirmed report of an active shooter.

At the same time, Brighton Police reported via Twitter that “there is a large police presence at Brighton High School after dispatch received a threatening call from an unknown person.”

About 9 a.m., Boulder officers asked residents to “avoid the area” of Arapahoe Avenue and 17th Street — just two blocks from the site of an active shooter situation with shots fired in, and near, the Millennial hotel on Monday off 28th and Arapahoe.

There is no evidence that the caller was ever on campus nor that there were any shots fired in the school.

Officers arrived on campus within three minutes, clearing the school and bringing in K-9 teams to check for possible bombs, said Herold, Boulder’s police chief.

There were no injuries and everyone is safe and out of the school, Herold said.

“It’s a long process, but we did it right and I’m proud of our response from all of our partners and Boulder Police Department,” Herold said. “This is the scariest kind of 911 call you can get, especially when you look across the country and see how many of these shootings are occurring.”

Boulder Valley School District spokesperson Randy Barber said law enforcement responded quickly and professionally, and Boulder High School followed protocol, putting the school on lockdown. Information was immediately sent to parents and staff, Barber said.

Boulder High was on a delayed start Wednesday morning and was scheduled to open at 9:35 a.m. Some students were already at the school for before-school activities, such as athletics, Barber said.

About 200 students — out of 2,025 total — were evacuated from the school Wednesday morning, Barber said, adding students were brought to CU Boulder’s Mackie Auditorium for reunification with family members.

“This is a horrific situation,” Barber said. “It’s the worst fear that most parents and most students have.”

The district trauma team was also activated to support students and other community, Barber said.

“We recognize the news coverage of this and being in school can be traumatic, especially given everything this city has gone through,” Barber said.

There are also resources at the reunification center for the students, Boulder Police Deputy Chief Stephen Redfearn added.

Officials do not know yet if the calls came from the same person or origin, Herold said, but they seem to have been systematic.

Alamosa Police Department got a call from a male person at 8:24 a.m., telling them that someone was walking into Ortega Middle School with an AR-style rifle, Alamosa Police Chief Ken Anderson said.

“We came to the conclusion pretty quickly that it was a hoax, but we can’t ignore it,” Anderson said.

Law enforcement from the Alamosa Police Department, Alamosa Sheriff’s Office and Adams State University responded to the call and “were there in a minute,” Anderson said.

“It’s pretty scary, it’s got to be spooky for the kids,” Anderson said. “It’s the second time this has happened this school year.”

“It is important to note that law enforcement will use all available resources to investigate a threat until we determine whether it is real or not,” an FBI spokesperson said. “Investigating hoax threats drains law enforcement resources and diverts officers from responding to an actual crisis.”

Swatting incidents across the country surged in the last few months. In Colorado, swatting closed the Denver Public Library in September and forced lockdowns at Denver’s East High School, Alamosa High School the Montrose School District and in Colorado Springs.

Experts anticipate such fake calls to keep hammering public places, notably schools.

Dr. Amy Klinger, co-founder and director of programs at the Educator’s School Safety Network, said schools can mitigate the effect of these calls.

Training, planning and communication can help prepare everyone for swatting incidents, she said, adding that, while no response to swatting will ever be perfect, preparation can make it less catastrophic.

“Every school is going to receive a false call at some point because it’s happening so frequently that schools need to be prepared for that,” Klinger said. “(Schools) can do training. They can plan. They can have conversations and discussions with their students and parents about response.”

The 2018-2019 school year saw 69 false reports or mock attacks out of 368 total incidents, according to data from the Educator’s School Safety Network. But from January to November, swatting calls stood at 175 out of 236 total incidents.

From Aug. 1 to Sept. 30, ESSN tracked 14 false reports of an active shooter event in 2019, and 99 such reports in 2022, a 607% increase.

Matthew Fulford, a social studies teacher in Denver, wrote about the psychological and emotional distress of one swatting incident at this school in September, which prompted a SWAT response.

“I first realized that this was no drill when I heard sirens and crawled over to the window. In front of the school was a full-blown SWAT response with dozens of police cars and armed officers with guns drawn running towards the building,” he wrote for Chalkbeat.

“I had positioned myself between students and the classroom door where police were shouting. Instructing the students to look at me and hold hands with one another, I told them that we were all going to be fine. At that point, a second door at the back of the room flew open revealing multiple officers pointing handguns at us. This led to universal shock as none of us had ever seen that door open before,” he said.

Fulford said educators understood that so many traumatized children in one place “created a crisis of its own.”

More information on swatting is located at fbi.gov.

Denver Gazette reporter Carol McKinley and Denver Gazette news partners 9News contributed to this story. Previous reporting by Chalkbeat is also included.