BROOKLYN CENTER, Minn. — Officer Kimberly A. Potter was in the middle of a routine training day on Sunday, demonstrating her decades of policing know-how to less experienced officers at the Brooklyn Center Police Department.

But that training came to an abrupt and horrifying end when Officer Potter, who is white, shot Daunte Wright, a Black 20-year-old guy, in his car as he tried to avoid arrest. Body camera video proves that the officer cried “Taser! ” whilst pointing a handgun in Mr. Wright, who was unarmed; she then fired a single round into his chest, killing him, in what the authorities in Minnesota have described as a deadly mistake.

Officer Kimberly A. Potter Charge…Bruce Bisping/Star Tribune, via Getty Images

With protests unfolding each night in Brooklyn Center, Officer Potter, a veteran officer of 26 years, and Tim Gannon, the department’s police chief, both resigned their posts on Tuesday. The abrupt departures came a day after the city manager who oversaw the department had been fired, and as the city of 30,000 residents remained boarded up; National Guard troops stood with guns beyond town ’s police station, that has been the center of nightly clashes.

Outside of Officer Potter’s home in a different Minneapolis suburb on Tuesday morning, police officers looked on as workers put concrete barriers and black metal fencing all around the house, fortifying it in a fashion like the courthouse in downtown Minneapolis, where Derek Chauvin, a former Minneapolis officer who had trained younger officers, is on trial in the passing of George Floyd.

Officer Potter, together with her decades on the force, was acting as a training officer, assigned to guide less experienced colleagues on Sunday night, a spokeswoman for the police union that represents her said, when Mr. Wright was pulled over for an expired registration on his vehicle.

The union that represents Officer Potter declined to comment on the events which followed, and her attorney, Earl Gray, said that she did not wish to talk. City officials did not respond to requests for her employment records.

In 1995, she was licensed as a police officer in Minnesota and took a job with the Brooklyn Center police. Officer Potter, 48, was the president of the police union recently, according to the Hennepin County Attorney’s Office.

Officer Potter graduated from Saint Mary’s University of Minnesota, a small Catholic school, in 1994 with a criminal justice major, a school official said.

There is no sign in available documents that she had shot anyone before. She was the police union president in August 2019, when she was among the first officers to arrive on the scene after two Brooklyn Center police officers shot and killed Kobe Dimock-Heisler, 21.

A report later concluded that Mr. Dimock-Heisler, that was described as mentally ill, had lunged at a police officer with a knife during a domestic disturbance call. Officer Potter advised all the officers to go into separate squad cars, switch off their body cameras rather than talk to each other, according to the report last year from the Hennepin County attorney. No charges were filed in the case.

Officer Potter’s husband, Jeffrey Potter, was also a police officer, serving in the Fridley Police Department in Minnesota for 28 years until his retirement in 2017. According to a community newsletter, Mr. Potter was an instructor in the department, training officers in use of force, Taser usage and crowd control.

In a letter Officer Potter delivered to city officials on Tuesday, she said she’d “loved every minute of being a police officer and serving this community to the best of my ability, but I feel it’s in the best interest of the community, the department and my fellow officers should I step immediately. ”

At a news conference announcing the departures, Mayor Mike Elliott acknowledged that of the nearly 50 police officers in the department, he knew of none who lived in town they patrolled.

We do feel very strongly that we want officers to be from the neighborhood, Mr. Elliott said. “People want justice. They want full accountability under the law. Thats what we will continue working for, ” he said.

The Bureau of Criminal Apprehension, a state agency in Minnesota, is conducting an investigation into Mr. Wright’s shooting, and the Washington County Attorney’s Office could bring charges against her.

Mr. Elliott also called for Gov. Tim Walz to move the case from the Washington County Attorney’s Office to the state attorney general, Keith Ellison, whose office is prosecuting Mr. Chauvin — a movement that seemed unlikely.

On Tuesday afternoon, city officials in Minneapolis and St. Paul invoked a curfew of 10 p.m., preparing for more protests in the day.

Tony Gruenig, a commander in the Police Department who was appointed acting chief of police on Tuesday, said he had not yet devised a strategy to respond to the anger in the community. Were just trying to wrap our heads around the situation and attempt to create some calm, he said.

For many in Brooklyn Center, though, the afternoon ’s resignations brought little hope of real change. Michelle Winters, a resident of nearby Brooklyn Park, said justice wouldn’t be served until police officers that killed people were charged like they were civilians.

They should charge them as they charge one of us, said Ms. Winters, who is Black and was standing facing the Brooklyn Center Police Department on Tuesday, where protesters were gearing up for another night of demonstrations. Regardless of what the mayor does, she said, residents will not be satisfied unless the police stop killing people.

Provided that you keep doing this and doing this over again, its not going to get better, she said. “I don’t care if they call in the National Guard every month, that’s not going to help anything. ”

Nicholas Bogel-Burroughs reported from Brooklyn Center, and Julie Bosman from Chicago. Stephanie Saul contributed reporting from Port Washington, N.Y. Kitty Bennett contributed study.