EVANSTON, Ill. (CBS) — One person was arrested and an officer was injured in clash between protesters and police in downtown Evanston this weekend.

The unrest happened Saturday night, as Northwestern University students called to abolish campus police.

As CBS 2’s Steven Graves reported, students on Sunday did not want to go on camera in fear of retribution from the school, but they said police were the aggressors – while officers said the opposite.

On Halloween Saturday night, windows were broken at the Whole Foods at 1640 Chicago Ave. Plants were left on the sidewalks, bikes were left abandoned, and graffiti was spray-painted on outside walls.

The aftermath remained hours later following clashes between police and Northwestern student protesters – whose push and stance was to get rid of campus police.

A few hundred students, nearly all from Northwestern, turned out for the event organized by a group called NU Community Not Cops. It started peacefully, but as the march went on, things changed.

Students shared a video with CBS 2 showing firecrackers used as a smaller group of students came face to face with Evanston police with backup from other local police departments.

Protesters have been marching in support of abolishing campus police that effort every day since Oct. 12, but students say a small group of demonstrators Saturday night turned more aggressive as they broke windows downtown, spray-painting buildings and launching those fireworks.

Evanston’s police chief says that is when officers moved in.

“”We allowed them to do a peaceful assembly and we would have let it ride until they turned to violence with bricks, battering some of our officers. They had shields,” said Evanston police Chief Demitrous Cook. “So after that it was time to send a message that we’re not going to let people just come in here and tear up the City of Evanston.”

On Sunday afternoon, Evanston police issued a news release with more specifics. Police said the group first gathered at Sheridan Road and Clark Street on the edge of the Northwestern campus, and then headed into downtown Evanston.

“The crowd marched into downtown Evanston, with some protesters throwing rocks and bricks at police officers, lighting fireworks in the direction of officers, pointing lasers at police officers’ eyes, and using umbrellas to cover individuals graffitiing streets, stop signs, and electric boxes, and damaging property,” Evanston police said in a news release.

Evanston police said they did use pepper spray to prevent injury to officers and bystanders, but contrary to claims on social media, they did not use tear gas.

“Smoke seen in any photos is from fireworks used by the protesters, not tear gas,” the release said.

One officer from the Northern Illinois Police Alarm System, which was called to the scene to assist, was injured and hospitalized with an eye injury with a firework, police said.

A female Northwestern student was arrested for hitting a police officer, police said. There were also 18 reports of criminal damage to property.

Students said the protester who was arrested has since been released.

But students who marched with NU Community Not Cops told CBS 2 the officers became violent toward them first.

They said the sheer number was excessive, and police used bikes to aggravate a calm situation.

On Sunday morning, Evanston Mayor Stephen Hagerty issued a letter to Northwestern President Morton Schapiro about ongoing protests in Evanston.

In part, the letter read: “While I believe many Evanstonians support a reexamination and reimagining of policing in America (as we are trying to do here in Evanston), our residents do not support protesters who are marching through the streets of Evanston at night throwing bricks, stones, or other objects at police officers, shooting fireworks in their direction, and intentionally damaging and defacing public property, all while hiding behind umbrellas and lasers aimed in the eyes of police officers. Protesters are not helping their cause by putting officers’ safety at risk and defacing and damaging public property, ironically all in a City that, while still very much a work-in-progress, is the first in America to create a reparations fund.”

Hagerty noted that the protest has been going on for 30 days and has cost tens of thousands, if not hundreds of thousands of dollars in overtime, which he wrote he “anticipated” Northwestern will cover.

“I, like you, want to know that these protesters are safe. It is always on my mind that the protester is someone’s child, and whether I agree or disagree with their efforts, they deserve to protest safely,” Hagerty wrote. “Likewise, I have a tremendous amount of respect for the officers who are keeping our sons and daughters safe, as well as protecting the property of our entrepreneurs and business owners. My expectation is that your administration will remind these Northwestern organizers that officers also have families and their safety is as important as the safety of the protesters.”

NU Community Not Cops calls on the university to defund police and “entrust the safety of the campus community in unarmed mediation and intervention teams with third-party oversight.”

Schapiro has come out against that idea before. Last month, Schapiro acknowledged these protests by students, saying while the university is always looking to improve its policing, they have no intention to abolish it.

On Sunday, the university said it supports peaceful protest, but not breaking the law.

CBS 2’s Marie Saavedra contributed to this report.