By Erin Ailworth, Sadie Gurman and Ben Kesling
MINNEAPOLIS -- Minnesota Gov. Tim Walz sent in the National Guard as demonstrators clashed with police for a third straight day to protest the death of George Floyd, a black man who died after a white officer pinned him to the ground with a knee on his neck in an incident captured on video.
Minneapolis Mayor Jacob Frey, who has called for the police officers involved in the incident to be criminally charged, had requested the assistance.
The Third Precinct police station, which has been a central site for demonstrations, was taken over and set on fire late Thursday, according to local news reports and video posted on social media.
Earlier, a large crowd gathered in a plaza outside the Hennepin County Government Center, waving signs, chanting George Floyd's name and calling for charges against the officers involved in his arrest. Those demonstrations started peacefully Thursday evening but turned tense when police officers in riot gear approached protesters who screamed at them. Police shot flash-bang grenades and tear gas into the crowds. Protesters marching through downtown, passing by a boarded up Lumber Exchange Building, shouted with their hands up in the air. Some poured milk into their eyes to ease the sting of the gas.
Protests in nearby St. Paul also turned violent, as some people smashed store windows.
Meanwhile on Thursday, calls for criminal charges continued to grow. Federal and state authorities have said they are investigating.
Hennepin County Attorney Mike Freeman, the official responsible for bringing charges, said that by itself, the video -- which has circulated on social media -- won't necessarily be enough evidence on which to base a criminal case.
"That video is graphic and horrific and terrible and no person should do that," he said. "But my job in the end is to prove that he violated criminal statute. And there is other evidence that does not support a criminal charge. We need to wade through all of that evidence to come to a meaningful determination and we are doing that to the best of our ability." Mr. Freeman didn't elaborate on the other evidence.
The officers aren't cooperating with the investigation, Mr. Freeman said.
The Justice Department said it has made the investigation a priority, assigning experienced prosecutors and FBI criminal investigators to the case to probe whether the officers willfully violated Mr. Floyd's civil rights. "It's really imperative that the community understands how seriously we're taking this and how swiftly we're moving on this," said U.S. Attorney Erica MacDonald.
Bringing federal civil-rights charges against police is a challenge, as prosecutors must reach a difficult standard of proof that requires them to establish that an officer not only acted with excessive force but also willfully violated someone's constitutional rights.
State prosecutors are able to pursue a wider array of criminal charges under state law, such as manslaughter or aggravated assault.
Protests spread Thursday to other cities, including New York, Denver and Chicago. More than 30 people were arrested on various charges at several protests around New York City on Thursday night, police officials said. The demonstrations, which began at Union Square in Manhattan, grew violent as one protester threw a garbage can at an officer and another punched an officer, according to the officials. Offshoot protests formed in locations around lower Manhattan, the officials said, including Zuccotti Park near Wall Street.
The majority of the mass-transit service in Minneapolis has been suspended through at least the afternoon and evening because of protests.
The mayor, a 38-year-old member of the Democratic-Farmer-Labor Party, said that the last several nights of unrest revealed 400 years of frustration in the black community. But he said it was critical that the city protect infrastructure like grocery stores, drugstores and banks that are necessary to protect health during the coronavirus pandemic.
Minneapolis Chief of Police Medaria Arradondo said there was a shift in tenor during the second night of protests with "a core group of people that had been focused on causing destruction."
Efforts to control the crowd broke down as it grew in size, he said. "We were certainly prepared for that immediate area," he said. "The crowds got larger, and they got more mobile."
The Minneapolis area has a history of tension between the African-American community and law enforcement, including the 2016 killing of Philando Castile, a black man, by a police officer in a nearby suburb. Months before that, the shooting of a black man in the city led to protests, including a Black Lives Matter encampment at a police precinct.
Mr. Arradondo became police chief in 2017 after an officer-involved shooting led to the resignation of his predecessor. In 2007, he was one of several officers who sued the police department over discrimination against officers of color. Mr. Frey helped develop a stronger policy on the use of police body cameras early in his term.
Leslie Redmond, president for the Minneapolis NAACP, said there is support in the community for the city's current chief of police, unlike with past chiefs.
"Chief Arradondo made the first right step in making sure the officers were fired and now he needs to move forward and make sure that they are charged because what we witnessed was murder," she said.
The four officers involved in the Monday incident were fired Tuesday morning.
In a Facebook video that emerged Tuesday, Mr. Floyd can be seen being pinned to the ground by an officer identified as Derek Chauvin, who has his knee on Mr. Floyd's neck. Other footage later emerged showing two other officers sitting on Mr. Floyd's body. Mr. Floyd is heard pleading that he can't breathe, and eventually loses consciousness. A fire department crew called to assist found paramedics working inside an ambulance on "an unresponsive, pulseless male," a fire department report said. Mr. Floyd was pronounced dead later that evening.
Two of the former officers who appear on the Facebook video, Mr. Chauvin and Tou Thao, each have multiple complaints on their official records, according to department records.
Mr. Chauvin has 18 complaints on his official record, two of which ended in discipline from the department including official letters of reprimand. Mr. Thao has six incidents on his record, including one stemming from a 2017 lawsuit that was settled by the city and which is still officially open in his record. The department declined to comment on the details of the complaints.
Mr. Thao was sued, along with another officer in 2017 for excessive use of force, a case whose final terms were sealed as terms of the settlement.
Tom Kelly, a lawyer for Mr. Chauvin, didn't respond to a request for comment.
Mr. Thao couldn't be reached for comment.
Minneapolis police said they arrested Mr. Floyd on Monday for using a counterfeit bill, and that he resisted arrest. Attorney Benjamin Crump, who is representing Mr. Floyd's family, said the man never resisted arrest and shouldn't have been treated so violently.
Alvin Manago and Theresa Scott, an engaged couple, remembered their friend and roommate, who liked to go by Floyd, as someone who "always tried to be the peacemaker," Mr. Manago recalled.
They said they were trying to forget the images in the Facebook video. Instead, they warmly recalled how he would burn everything he tried to cook, even hot dogs. How he liked to sing when he was happy. How his laugh was a slow-building, full-body chuckle.
--Joe Barrett and Ben Chapman contributed to this article.
Write to Erin Ailworth at Erin.Ailworth@wsj.com, Sadie Gurman at email@example.com and Ben Kesling at firstname.lastname@example.org