MINNEAPOLIS — Authorities on Wednesday upgraded murder charges against the former Minneapolis police officer who pinned George Floyd to the ground by his neck, while charging three other former officers who were at the scene with aiding and abetting the killing.

The charges carry maximum sentences of as many as 40 years for all four officers, according to criminal complaints released Wednesday. But the arrests did little to deter nearly 10 days of nationwide protests in the wake of Floyd’s death or to quell calls for fundamental changes to policing. The charges only deepened demands in Minneapolis to overhaul the embattled police department or abolish it altogether.

Minnesota Attorney General Keith Ellison acknowledged the uphill battle in prosecuting murder charges against police officers, who rarely are convicted of on-duty killings, but said he is confident that the facts of the case support the charges.

“George Floyd mattered. He was loved. His family was important. His life had value,” Ellison said in announcing the new charges. “We will seek justice for him and for you, and we will find it.”

Derek Chauvin, the 44-year-old white officer who was captured on video kneeling on Floyd’s neck for nearly nine minutes as the black man pleaded for air, now faces a charge of second-degree murder, in addition to the third-degree murder charge officials filed last week.

Thomas Lane, Tou Thao and J. Alexander Kueng, who were fired along with Chauvin in the wake of the incident, face charges of felony aiding and abetting second-degree murder and second-degree manslaughter. Their charges carry the same potential sentences as Chauvin’s, including a maximum 40-year prison sentence for second-degree murder. Bail for all four was set at $1 million.

Ellison made the announcement during an afternoon news conference days after being appointed by Gov. Tim Walz (D) to take over the investigation from the Hennepin County Attorney’s Office. Floyd’s family had been joined by some city council members and activists in asking for Ellison to take the lead.

Floyd’s family had repeatedly called for the arrests of the other three officers involved in the encounter outside the Cup Foods corner store, which began when the 46-year-old father and security guard was accused of using a counterfeit $20 bill. On Wednesday, Floyd’s son Quincy Mason visited the growing memorial outside the store with family attorney Ben Crump and demanded accountability, saying that “no man or woman should be without their fathers.”

In a statement released through its attorney, the family called news of the charges “bittersweet” and expressed gratitude that Ellison “took decisive action in this case.”

“This is a significant step forward on the road to justice, and we are gratified that this important action was brought before George Floyd’s body was laid to rest,” the statement said. “That is a source of peace for George’s family in this painful time.”

Ellison pushed back on suggestions that public pressure factored into his charging decisions. But he acknowledged that punishing those involved could not fix the systemic racism that has long plagued the country and fueled protests from coast to coast.

“I don’t believe one successful prosecution can reflect the hurt and loss that people feel,” he said.

He urged citizens, activists and leaders in government and faith communities to “begin rewriting the rules for a just society now,” as the criminal case pends.

The new charges followed days of protests and unrest that started in Minneapolis and spread across the nation. Throngs of demonstrators have flooded the streets of dozens of U.S. cities, with large demonstrations against police violence unfolding anew on Wednesday. Elected leaders have struggled to cope with the damage already done — civilians injured by police, police hurt by civilians and looters who used the mostly peaceful protests as cover, prompting officials in multiple states to set curfews and call in the National Guard.

In footage of the encounter between Floyd and the four officers, Lane and Kueng helped Chauvin hold down the handcuffed man, leaning on his back and legs, while Thao stood watch as an increasingly distraught crowd of onlookers protested that Floyd could not breathe. Lane at least twice asked if Floyd should be rolled to his side, a suggestion that Chauvin rebuffed, according to court records.

The Hennepin County Medical Examiner released a full autopsy report Wednesday, finding Floyd’s death to be a homicide — agreeing in broad strokes with an independent autopsy commissioned by Floyd’s family, who had said they did not trust authorities’ findings.

Floyd had also tested positive for the coronavirus in April, the report reveals. The autopsy found Floyd likely had “asymptomatic but persistent … positivity” from that past infection, the report states.

Records released by the Minneapolis Police Department show that Chauvin had at least 17 conduct complaints filed against him throughout his 19-year tenure. All were closed without discipline except for two, which were sustained and resulted in letters of reprimand.

He was involved in at least three shooting incidents, including one in 2006 in which he and five other officers fatally shot Wayne Reyes, a stabbing suspect. In two of the cases, he received medals of valor or commendation from the department, according to his personnel file.

Thao, 34, had faced at least six conduct complaints, all closed without discipline except for one still active at the time of his firing. In 2017, he was the subject of a civil rights lawsuit alleging that he and another officer beat a man they were arresting. The city settled the case for $25,000.

Kueng, 26, and Lane, 37, were rookies in the department, both receiving their law enforcement license in August. Neither had a history of complaints.

Attorneys for the officers did not respond Wednesday to calls seeking comment. Efforts to reach the officers and their family members have been unsuccessful.

Lt. Bob Kroll, president of the Minneapolis police union, has not responded to multiple requests for comment but said in a letter to union members Monday that the officers were terminated “without due process.”

A Washington Post reporter who knocked on Kroll’s door was soon pulled over by a police officer who said that Kroll had reported suspicious activity on his front porch and that “he doesn’t want any press.”

Charges against officers are rare, and convictions even rarer. Since 2005, 110 nonfederal law enforcement officers in the United States have been arrested for murder or manslaughter for shooting someone on duty, according to a tally kept by Philip Stinson, a Bowling Green State University professor. From those ranks, five have been convicted of murder, five of homicide and another 22 of manslaughter.

In one of the most high-profile police shootings in recent years, a white Chicago police officer shot and killed Laquan McDonald, a black teenager, in 2014. Jason Van Dyke, the now-former officer, was convicted of second-degree murder in 2018.

But outside of that case, it’s highly unusual for a police officer to face second-degree murder charges, said Robert Weisberg, a criminal justice expert and law professor at Stanford University. He emphasized that Floyd’s death stands out from many police killings that have attracted nationwide attention, given Chauvin knelt on Floyd’s neck for more than eight minutes as he lay handcuffed, eventually going limp — in contrast to police shootings in which an officer argues they felt threatened and acted in self-defense.

With charges of aiding and abetting — which carries the same weight as Chauvin’s second-degree murder charge — the attorney general has indicated that he believes the other three officers were not merely negligent, Weisberg said.

“The attorney general is really saying, it was Chauvin’s knee on Mr. Floyd’s neck, but they were all in effect putting their knees on his neck,” Weisberg said.

The charges related to second-degree murder require the prosecutors to show that, while the officers might not have meant to kill Floyd, they did intend to commit the underlying felony of the aggravated assault, said Mark Osler, a law professor at the University of St. Thomas in St. Paul.

Ellison noted that the Hennepin County Attorney’s office, which originally was handling the case, is the only one in the state to have secured a murder conviction for a police officer. He warned that the case could take months as prosecutors strive for thoroughness because “winning a conviction will be hard.”

“I say this not because we doubt our resources or our ability. In fact, we’re confident in what we’re doing,” Ellison said. “But history does show that there are clear challenges here.”

First-degree murder charges, which Floyd’s family and some protesters have called for, would be far harder to prove, requiring premeditation ⁠ — reflection and planning before taking the fatal action, Osler said.

“I understand why people reach the term first-degree murder, because they’re making a perfectly plausible moral statement that this is as horrendous a crime as you can imagine,” Weisberg said. “But first-degree murder is not a moral term. It’s a technical, legal term.

Floyd’s death was the latest in a string of high-profile killings by officers in the Minneapolis region in recent years. In 2015, weeks of demonstrations followed the death of Jamar Clark, a 24-year-old black man shot by a Minneapolis police officer shot. Local and federal officials declined to charge the officers involved.

The following year, the shooting death of Philando Castile during a traffic stop was captured in a graphic video streamed by his girlfriend, who sat in the passenger seat with her daughter in the back. The officer, who worked for a suburban police department, involved was charged with manslaughter and acquitted.

Then, in 2017, Justine Damond, a white Australian woman, was fatally shot by the Minneapolis police officer who responded to her call about what she believed was a possible sexual assault near her home. He was convicted of murder last year.

Floyd’s killing has brought intensified scrutiny on the Minneapolis Police Department, with some calls to abolish the force. It’s a radical idea that has been around for decades but is gaining momentum in a city outraged over the killing of Floyd.

In Minneapolis, and in cities across the country, this shift would likely begin with the municipal budget. The city council and Mayor Jacob Frey (D) increased spending on police in 2020, earmarking $193 million, or about 12 percent of the city’s budget, for the department. But recovering from days of unrest, the 13-member council has begun discussing whether it should cut funding.

“Several of us on the council are working on finding out what it would take to disband the MPD and start fresh with a community-oriented, nonviolent public safety and outreach capacity,” council member Steve Fletcher said in a lengthy Twitter thread. “The whole world is watching, and we can declare policing as we know it a thing of the past, and create a compassionate, nonviolent future.”

Already, the Minneapolis school district has said it will no longer have city police serve as school resource officers, and the University of Minnesota has said it plans to scale back its ties with the department.

Wednesday’s additional charges were welcomed by Walz, who said in a statement that they were “a meaningful step toward justice for George Floyd.” But, he added, “we must also recognize that the anguish driving protests around the world is about more than one tragic incident.”

Floyd’s family also said that more work is needed. Family members said in their statement that the four officers “knew they could act with impunity,” claiming there is a pattern of civil rights violations within the Minneapolis Police Department. They called for accountability at all levels of policing.

“We are deeply grateful for the outpouring of support by Americans in cities across the country, and we urge them to raise their voices for change in peaceful ways,” they said. “Our message to them is: Find constructive and positive ways to keep the focus and pressure on. Don’t let up on your demand for change.”

There was little sign of the demands for change easing in Minneapolis, where the news of the heightened murder charge against Chauvin and the felony charges against the three other officers brought a measure of relief, but little cause for celebration.

“It shouldn’t have taken this long,” said Ernest Howard, 46, a South Minneapolis native who has been protesting each day since he saw the video of Floyd.

“I applaud them for charging those four officers,” said Mike Griffin, an organizer with Community Change Action who has participated in the Minneapolis protests. “But in order for us to [prevent] the next black guy from being killed three months from now, six months from now or a year from now, we need to change these systemic problems.”

Ultimately, Griffin added, “our power to change these systemic problems is going to come on the ballot the first week of November.”

At a downtown rally Wednesday, activist and civil rights lawyer Nekima Levy Armstrong told a boisterous crowd that even though the four officers involved finally face charges, critical legal and societal battles remain.

“We have to continue to be vigilant,” she said. “We can’t rest just because they finally did what was supposed to have been done.”

Outside the Cup Foods at E. 38th Street and S. Chicago Avenue, where a large blue and white angel has been drawn on the spot where Floyd was pinned to the ground, hundreds of people gathered as the officers’ charges were announced. Chalk art and flowers lined the sidewalk, and a freshly painted mural of Floyd adorned the side of a building, with a caption that read, “I can breathe now.”

Standing quietly near the memorial was Michael Brown Sr., whose 18-year-old son Michael Jr. was fatally shot by a police officer in Ferguson, Mo., six years ago this summer. Brown, who now is an avid activist for police reforms, said he felt encouraged by the speed in which the officers were fired and charged.

“It gives people hope that change can come, that people making bad decisions and getting away with it will finally be stopped,” he said, adding that only time will tell if this was truly a moment of transformation.

Floyd’s son, Mason, also visited the site Wednesday, kneeling at the spot where his father last gasped for air. He thanked demonstrators for their displays of solidarity.

“I’m trying to get justice for my father. No man or woman should be without their fathers,” Mason said, adding: “We need change. It can’t happen to anybody else.”

Crump, the Floyd family attorney, joined Mason in addressing the crowd and called not only for accountability in Minneapolis, but for deeper and more lasting changes.

“We cannot have two justice systems in America — one for black America and one for white America,” he said. “We must have equal justice for the United States of America.”

Sheila Regan, Tarkor Zehn, Robert Klemko and Holly Bailey in Minneapolis and Hannah Knowles, Reis Thebault, Katie Mettler, Brittany Shammas, Mark Berman, Kim Bellware, Meryl Kornfield, Julie Tate and Lateshia Beachum in Washington contributed to this report.