MINNEAPOLIS (AP) — The mayor of Minneapolis called Wednesday for criminal charges to be filed against the white police officer seen on video kneeling on the neck of a handcuffed black man during an arrest, even after the man said he couldn’t breathe and stopped moving.

Based on the video, Mayor Jacob Frey said he believes officer Derek Chauvin should be charged in Monday’s death of George Floyd. Chauvin and three other officers were fired Tuesday. The video recorded by a bystander shows Chauvin with his knee on Floyd’s neck for several minutes as Floyd is on the ground with his face against the pavement.

“I’ve wrestled with, more than anything else over the last 36 hours, one fundamental question: Why is the man who killed George Floyd not in jail?” said Frey, who is white.

He later added: “I saw no threat. I saw nothing that would signal that this kind of force was necessary.”

But despite the officers’ swift dismissals, whether the death will be considered a criminal act or something less, like excessive force, is a more complicated question that will likely take months to investigate.

Floyd’s death prompted protests Tuesday, with thousands taking to the streets at the intersection where he died.

Many protesters marched more than 2 miles to the police precinct station in that part of the city, with some damaging the building’s windows and squad cars and spraying graffiti. Police in riot gear eventually confronted them with tear gas and projectiles. Tense skirmishes stretched late into the evening.

Bridgett Floyd told NBC’s “Today” show that the officers involved in her brother’s death should be charged with murder because “that’s exactly what they did.” She said she had not watched the video, but she told ABC’s “Good Morning America” that she does not understand “how someone could possibly let an individual go out like that.”

The FBI and state law enforcement were investigating Floyd’s death, which immediately drew comparisons to the case of Eric Garner, an unarmed black man who died in 2014 in New York after he was placed in a chokehold by police and pleaded for his life, saying he could not breathe.

The officers in the Minneapolis case have not been publicly identified, though one defense attorney has confirmed he is representing Chauvin. The attorney, Tom Kelly, declined to comment further.

The police union asked the public to wait for the investigation to take its course and not to “rush to judgment and immediately condemn our officers.” Messages left with the union after the firings were not returned.

During Tuesday’s protests, some chanted and carried banners that read, “I can’t breathe” and “Jail killer KKKops.” Some stacked shopping carts to make a barricade at a Target store across the street from the station.