By the time police arrived, the party had been raging for hours.

Beginning late Saturday afternoon, music bumped as 500 to 800 maskless revelers swarmed a street in a neighborhood near the University of Colorado at Boulder. The cheering crowd later blasted fireworks into the sky and flipped a car.

Law enforcement officers showed up with a SWAT vehicle at about 8:30 p.m. local time. Using a loudspeaker, they warned: “If you fail to leave, you will be subject to arrest and the use of tear gas.” Many students cleared out. Others stayed, shouting expletives at police. About 100 ran toward authorities, police said, and several threw bottles and rocks.

The chaos, which unfolded a day after Colorado Gov. Jared Polis (D) paid tribute to the state’s nearly 6,000 coronavirus victims, ended with police reporting minor injuries to several officers, along with damage to community and public safety vehicles.

Authorities said Sunday that they were poring over images from the night and starting a website to collect tips from the public. They promised serious consequences for those involved in the incident, condemning it as selfish and dangerous — especially at a time when virus cases have been trending down.

“I hear people refer to it as a party,” Boulder County District Attorney Michael Dougherty said at a news conference. “I don’t regard people flipping over a car as a party. I don’t regard people throwing bottles and rocks at firefighters and police officers as a party. Those are criminal acts and will be treated as such.”

Throughout the pandemic, tensions have flared on college campuses as administrators try to keep in-person classes in session while discouraging partying among students. Some schools have attempted to shut down socializing, while others go as far as expelling those who break the rules.

More than 535,000 infections have been linked to colleges, according to a New York Times tracker, including 120,000 since the start of this year. Cases have recently been on the decline in college towns, just as they have across the United States as a whole.

In a video snippet posted online from the Boulder event, a partyer could be heard saying, “This feels good. Boulder’s back, baby!” As the camera panned over students standing shoulder-to-shoulder in the street, someone responded, “Finally.”

But Boulder County Public Health Executive Director Jeff Zayach said such behavior threatened to undo hard-won improvements in local case numbers. The county was averaging about 50 new infections per day last week, compared with a high of about 220 in November, according to a Washington Post database.

“Now is not the time to do these kind of things,” Zayach said.

What started out as a party ultimately turned into a violent and dangerous crowd, officials said. Even absent a pandemic, they added, it wouldn’t have been allowed in a residential neighborhood.

Chief Maris Herold said police tried to clear the street before calling for assistance from other law enforcement agencies as the night wore on. They used what she described as “a limited amount” of tear gas and a long range acoustical device, but she said they were hesitant to use other force, not wanting to further agitate the crowd.

Several officers were injured after being hit by items tossed from the crowd. Herold said one could have been seriously hurt, “but thank God he had a gas mask on, and the gas mask took the majority of the blow to this officer’s face.” The windshield of the department’s SWAT vehicle was broken and its sides dented, and other vehicles damaged. Some in the crowd jumped on a fire engine as it was moving, police said.

Herold said authorities on the scene made “a very restrained, calculated call” that it was too dangerous to enter the crowd to make arrests.

“But believe me, we have excellent body-worn camera video, the community is sending us video,” Herold said. “There will be arrests.”

Students organized a cleanup of the street on Sunday, picking up smashed cans and broken glass left. Hailey Breaker, a senior, told the Boulder Daily Camera that the revelers “didn’t necessarily consider the consequences” and that she was disappointed by what occurred.

University officials, meanwhile, apologized on behalf of the students involved, with Chief Operating Officer Patrick O’Rourke saying their actions were “unacceptable on every level.” He said those who participated in violence against police and first responders will be expelled from the school. In-person classes will still be held this week as administrators monitor cases and urge students present Saturday to get tested for the virus.

“What we need is for all of our students to realize that the pandemic is not over,” O’Rourke said. “And we must stay vigilant to protect our community.”

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