CNN — Six people were arrested Saturday evening in downtown Atlanta, authorities said, during protests that came in response to a proposed police training facility and the fatal police shooting of an activist earlier in the week.

The protesters marched in a “peaceful manner” down a central Atlanta street but a group within the crowd later began “committing illegal acts,” including breaking windows and attacking police cruisers, Atlanta Police Chief Darin Schierbaum said in a news conference.

Police arrested six people and were continuing to investigate whether there were any others involved in illegal activity, the chief said. Three businesses sustained damage to their windows, he added.

Social media footage showed a police cruiser on fire in the downtown area, and video from CNN affiliate WANF showed broken windows at a Wells Fargo bank.

The protests come in response to a planned $90 million, 85-acre law enforcement training facility – dubbed “Cop City” by its opponents – and just days after the police killing of 26-year-old activist Manuel Esteban Paez Terán near the site of the training center.

The Wednesday killing was “indicative of a level of extreme escalation by the police,” said Sean Wolters, who is working within the broad coalition of the “Defend the Atlanta Forest” movement, which opposes the facility.

The Saturday protests aimed to bring awareness to the Atlanta Police Foundation and some of the entities tied to it, Wolters said.

“Why are we even talking about a few windows really, when we should be focused on the life of (Terán) and what he stood for and investigating what happened to him independently?” Wolters told CNN by phone on Sunday morning.

Some of the people arrested Saturday have “already been involved in other criminal activity and are involved in a manner to deter the building of the public safety training center,” Schierbaum, the police chief, said.

“My message is simple to those who seek to continue this type of criminal behavior,” Mayor Andre Dickens said during the news conference. “We will find you and we will arrest you and you will be held accountable.” Dickens was among the city council members who voted in favor of the training center in 2021.

Georgia Gov. Brian Kemp said on Twitter “violence and unlawful destruction of property are not acts of protest. They are crimes that will not be tolerated in Georgia and will be prosecuted fully.”

During the news conference, Dickens said many of those arrested “don’t even live in Atlanta or in the state of Georgia” and some were found “with explosives.”

Wolters told CNN there are people across the US who have traveled to the state to join the protests in opposition to the planned training facility and that it is “their constitutional right to do so.”

Slain activist’s mother feels angry and ‘powerless’

The activist’s fatal police shooting unfolded Wednesday morning, during what authorities said was a clearing operation to remove people from the site of the future facility. Opponents of the center have camped out in the area for months in an attempt to halt construction.

The Georgia Bureau of Investigation said law enforcement officers spotted an individual in a tent in the woods and gave verbal commands, but the individual allegedly did not comply and shot a Georgia State Patrol trooper, according to a news release.

Officers returned fire and fatally wounded the individual. A handgun recovered from the individual’s possession matched the projectile from the trooper’s wound, the GBI said.

Activists associated with movements protesting the facility, who dispute law enforcement’s account, said Terán was a “forest defender” working to fight environmental racism. Local justice groups said Terán, known as Tortuguita and who identified as nonbinary, was a “sweet, warm, very smart and caring” person.

“It’s a very emotionally heavy time,” Wolters, with the forest defenders’ movement, said. “Tortuguita was a very committed forest defender and very brave so a lot of people are still grieving,” Wolters said, adding there have been vigils for the activist in locations across the US over the past few days.

Terán’s mother told CNN by phone Saturday night that she felt angry and powerless over Terán’s death.

Speaking from Panamá City, Panamá, Belkis Terán expressed her disbelief in law enforcement’s recounting of the incident, saying “I know they said he shot first, but I don’t believe it.”

“He was attacked,” she added.

The mother said while law enforcement said Terán had a gun, she was not aware of the activist having one and that, “if he had one, it was for protecting himself against the animals in the forest. That’s what I understand.”

“He was not a violent person. He was a pacifist. He would tell me that all the time. ‘I am a pacifist.’ He wouldn’t even kill an animal,” Belkis Terán told CNN. “Tortuguita,” the nickname Terán went by, was because of their love for turtle conservation, the mother said.

She described Terán as a generous, “sweet soul” who from a young age always helped others.

Authorities will not identify trooper

The injured trooper was taken to a local hospital for surgery and was in stable condition Wednesday night, authorities said. The Georgia Department of Public Safety said it will not release the trooper’s name because “disclosure would compromise security against criminal or terroristic acts due to retaliation.”

Additionally, the GBI said that during its clearing operation on Wednesday it found and removed about 25 campsites and arrested and charged seven people with domestic terrorism and criminal trespass.

Authorities recovered “mortar style fireworks, multiple edged weapons, pellet rifles, gas masks and a blow torch,” it added.

A controversial facility

The Atlanta Police Foundation has said the planned training center is needed to help boost morale and recruitment efforts, and previous facilities used by law enforcement are substandard.

But the facility, which will include a shooting range, mock city and burn building, has been met with fierce resistance.

While some critics of the project see it as a response to the 2020 police brutality and racial injustice protests, city leaders have said the center will also help address police reform but have not provided further details.

Some residents have accused the city of blindsiding neighbors with what they said has been a largely secretive development process with little community input. Taxpayers will foot about $30 million of the facility’s cost, with the rest coming from private philanthropic and corporate donations, city officials have said.

And activists have also long expressed concern over the project’s environmental impact: The training center would carve out a chunk of forested land and fragment what local advocates hope will become a network of connected green spaces across parts of Atlanta and DeKalb County.

CNN’s Sharif Paget and Pamela Kirkland contributed to this report.