Prince George’s County has agreed to pay the family of a man fatally shot by a police officer $20 million in what is believed to be among the nation’s largest one-time settlements involving someone killed by law enforcement.

The county settled with the family of 43-year-old William Green, who authorities say was shot six times with his hands cuffed behind his back in the front seat of a police cruiser by Cpl. Michael A. Owen Jr.

Owen was arrested the day after the Jan. 27 shooting and has been suspended without pay. He is awaiting trial on charges of second-degree murder.

The agreement was reached between the administration of Prince George’s County Executive Angela D. Alsobrooks (D) and longtime Baltimore-based attorney William H. “Billy” Murphy.

“I agree with County Executive Alsobrooks that this historic settlement shows that the Black life of William Green and the Black lives of his grieving mother, son and daughter truly matter,” Murphy said. “Black lives matter.”

At a news conference Monday, Alsobrooks said the settlement represented the county “accepting responsibility” for mistakes made in Green’s death.

“Police are given by this community an awesome and tremendously difficult responsibility of protecting life,” she said. “They are also likewise given an authority that is not shared by anyone else in this community — and that is the authority to take life. . . . When that trust is abused, it is necessary to take swift and decisive action.”

The Green family’s settlement follows other payments in the wake of homicides involving on-duty police officers. This month, Louisville agreed to pay $12 million to the family of Breonna Taylor after she was fatally shot by police who raided the 26-year-old woman’s home. The death was one of several police killings of Black people that have fueled protests nationwide.

In 2015, Murphy secured a $6.4 million settlement with the city of Baltimore after the death of 25-year-old Freddie Gray in police custody.

The $20 million Prince George’s settlement is one of the biggest involving an African American killed by an on-duty officer in the United States, Murphy said. Those involved with the case said the hefty settlement was driven largely by the unprecedented details of the shooting, previously reported by The Washington Post, including red flags the department missed related to Owen’s history of using force and claims seeking workers’ compensation for psychological difficulties.

Alsobrooks said the $20 million will come from the county’s budget and had to be first approved by the county’s budget director.

“This is not the way we want to spend tax dollars, which is why we are doing everything we can to make sure it never happens again,” Alsobrooks said.

During the news conference in the county government office building in Largo, members of Green’s family joined Murphy, Alsobrooks and other officials. Shelly Green, Green’s daughter, said that while the settlement would never bring her father back, the family planned to use part of it to combat police brutality.

Green’s cousin Nikki Owens said the family was still grieving.

“This doesn’t bring justice,” she said of the settlement. “This doesn’t bring peace.”

On the evening Green was killed, police received a 911 call about a man driving a Buick who had struck several vehicles, starting in Silver Hill, Md. They found Green in the car nearby in Temple Hills.

Owen got Green out of the car, cuffed Green’s hands behind his back and placed him in the cruiser to wait for a drug recognition expert, according to police records and interviews. Owen is accused of firing seven shots a few minutes later, six of which hit Green, still handcuffed in the front seat.

Green, a father of two who worked as a Megabus luggage loader, was pronounced dead at a nearby hospital. The next day, Owen was arrested and charged in Green’s killing. Owen is the county’s first police officer charged with murder while on duty, Alsobrooks said.

Owen, who was not wearing a police-issued body camera at the time of the shooting, told authorities that he had feared for his life because Green reached for his firearm. Prosecutors say there is no evidence that Green posed a serious threat.

On Monday, Owen attorney Thomas Mooney called the prosecutor’s decision to charge his client a “knee-jerk” reaction based on “unsubstantiated or discounted facts and hastily misguided assumptions.” Mooney said Owen looked forward to his trial, “where all the facts will be finally revealed and brought to light and justice will prevail.” Owen remains jailed until trial.

An investigation by The Post showed that the county police department’s early-warning system flagged Owen for using force twice in quick succession the summer before Green’s killing. But his supervisors were not formally notified until January, The Post found, and they did not take action ahead of Green’s killing.

Owen’s supervisors were unaware that he had sought workers’ compensation for psychological difficulties stemming from a fatal shooting early in his career, department officials said, even though Owen was supposed to notify them.

Green was at least the second person killed by Owen. On Dec. 17, 2011, Owen fatally shot 35-year-old Rodney Deron Edwards after Owen saw Edwards lying in a front yard in Landover, according to police. When Owen tried to investigate, Edwards pulled a gun, according to Owen’s written report. Owen shot Edwards. Edwards’s family disputed the account, although a loaded handgun was found at the scene.

It is unclear whether Owen was involved in another fatal shooting. He filed a state workers’ compensation claim as a result of the fatal shooting of a suspect in 2010. But police have said that they have no record of Owen’s being involved in a fatal shooting on that date. Owen began seeing a psychiatrist as a result of that shooting, workers’ compensation records show.

Alsobrooks said officials have closed the loophole that allowed Owen to receive workers’ compensation for post-traumatic stress disorder without his bosses knowing at the same time as he continued working — a lapse detailed in The Post’s investigation. She added that she created a police reform group dedicated to making significant recommendations to the department and that she will be engaged in discussions at the state level this winter.

Retired Prince George’s County circuit judge Steven Platt, who served as the mediator in the case, said both sides recognized the facts were “uniformly bad” — and in fact worse than many higher-profile shootings and instances of police brutality that have occurred elsewhere in the country. Citing the Post investigation, Platt said warning signs about Owen missed by the department partly drove the settlement.

Murphy added that had the civil case gone to trial, the results could have been “catastrophic” for the county. But he said the family did not want to wait years for a trial to unfold, so a settlement was in the best interests of both parties.

Alsobrooks will issue a letter to the Green family “expressing regret the incident occurred” as part of the settlement and will allow the family to address the police-reform work group, the county said.

The Green settlement matches the amount the city of Minneapolis paid the family of Justine Ruszczyk last year after one of its officers at the time, Mohamed Noor, fatally shot the 40-year-old, unarmed White woman when she approached his car while he responded to her 911 call.

Noor’s attorneys argued at trial last year that he had fired his weapon to protect his frightened partner after hearing a noise and seeing a person by the driver-side window raising an arm. A jury later found Noor guilty of third-degree murder and second-degree manslaughter. A judge sentenced him to more than 12 years in prison.

Owen’s criminal trial is set for March.

Steve Thompson contributed to this report.