WASHINGTON (AP) — The Justice Department is opening a sweeping investigation into policing practices in Minneapolis after a former officer was convicted in the killing of George Floyd there, Attorney General Merrick Garland announced Wednesday.

The decision comes a day after former officer Derek Chauvin was found guilty of murder and manslaughter in Floyd's death last May, setting off a wave of relief across the country. The death prompted months of mass protests against policing and the treatment of Black people in the U.S.

The Justice Department was already investigating whether Chauvin and the other officers involved in Floyd's death violated his civil rights.

"Yesterday’s verdict in the state criminal trial does not address potentially systemic policing issues in Minneapolis," Garland said.

The new investigation is known as a “pattern or practice" — examining whether there is a pattern or practice of unconstitutional or unlawful policing — and will be a more sweeping probe of the entire police department and may result in major changes to policing there.

It will examine the use of force by police officers, including force used during protests, and whether the department engages in discriminatory practices. It will also look into the department’s handling of misconduct allegations and its treatment of people with behavioral health issues and will assess the department's current systems of accountability, Garland said.

It’s unclear whether the years under investigation will begin when Floyd died or before. Garland said a public report would be issued, if the department finds a pattern or practice of unconstitutional policing. The department could also bring a lawsuit against the police department, which in the past have typically ended in settlement agreements or consent decrees to force changes.

The Minneapolis Police Department is also being investigated by the Minnesota Department of Human Rights, which is looking into the department’s policies and practices over the last decade to see if it engaged in systemic discriminatory practices.

Minneapolis Mayor Jacob Frey said city officials “welcome the investigation as an opportunity to continue working toward deep change and accountability in the Minneapolis Police Department.” The city council also issued a statement supporting the investigation, saying its work had been constrained by local laws and that it welcomes “new tools to pursue transformational, structural changes to how the City provides for public safety.”

Floyd, 46, was arrested on suspicion of passing a counterfeit $20 bill for a pack of cigarettes at a corner market. He panicked, pleaded that he was claustrophobic and struggled with police when they tried to put him in a squad car. They put him on the ground instead.

The centerpiece of the case was bystander video of Floyd, handcuffed behind his back, gasping repeatedly, “I can’t breathe,” and onlookers yelling at Chauvin to stop as the officer pressed his knee on or close to Floyd’s neck for what authorities say was about 9 1/2 minutes, including several minutes after Floyd’s breathing had stopped and he had no pulse.

Floyd's death May 25 became a flashpoint in the national conversation about the deaths of Black Americans at the hands of law enforcement and sparked worldwide protests.

At trial, Chauvin's defense attorney persistently suggested Chauvin’s knee wasn’t on Floyd’s neck for as long as prosecutors argued, suggesting instead it was across Floyd’s back, shoulder blades and arm.

The decision to announce a sweeping Justice Department investigation comes as President Joe Biden has promised his administration would not rest following the jury's verdict in the case. In a Tuesday evening speech, he said much more needed to be done.

“‘I can’t breathe.’ Those were George Floyd’s last words,” Biden said. “We can’t let those words die with him. We have to keep hearing those words. We must not turn away. We can’t turn away.”

The Justice Department had previously considered opening a pattern or practice investigation into the police department soon after Floyd’s death, but then-Attorney General Bill Barr was hesitant to do so at the time, fearing that it could cause further divisions in law enforcement amid widespread protests and civil unrest, three people familiar with the matter told the AP.

Garland said the challenges being faced “are deeply woven into our history.”

"They did not arise today or last year,” Garland said. “Building trust between community and law enforcement will take time and effort by all of us, but we undertake this task with determination and urgency knowing that change cannot wait."

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Forliti contributed to this report from Minneapolis.

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Find AP’s full coverage of the death of George Floyd at: https://apnews.com/hub/death-of-george-floyd.