MEMPHIS, Tenn. (AP) — The family of Tyre Nichols, who died after a brutal beating by five Memphis police officers, sued the officers and the city of Memphis on Wednesday, blaming them for his death and accusing officials of allowing a special unit’s aggressive tactics to go unchecked despite warning signs.

The federal suit filed by lawyers for Nichols’ mother, RowVaughn Wells, seeks a jury trial and financial damages.

“It’s my turn to make sure that my son’s death does not go in vain,” Wells said at a news conference Wednesday. “This has nothing to do with the monetary value of the lawsuit, but everything to do with accountability. Those five police officers murdered my son. They beat him to death and they need to be held accountable.”

The lawsuit claims the SCORPION unit launched by Memphis Police Director Cerelyn “CJ” Davis used “extreme intimidation, humiliation, and violence” and “disproportionately focused on and targeted young Black men.” It says that the department permitted this aggressive approach and ignored complaints by others targeted before Nichols’ death.

The five officers charged with beating the 29-year-old were members of the unit, which has since been disbanded, police have said.

Civil rights attorney Ben Crump, who is representing the family, said the lawsuit is asking for $550 million. Another family lawyer Antonio Romanucci said the amount symbolized the 55 years since Martin Luther King Jr. was killed in Memphis.

The lawsuit is meant to send a message to other cities, Crump said. “We will bring these lawsuits to other cities where police are killing Black and brown people,” he said. “If it happens in your city, we’re coming to your city too,” adding that their mission is to make it unaffordable for police to continue to have these police units.

The city and the Memphis Police Department declined comment.

Nichols died three days after the beating in January. It was the latest in a string of violent encounters between police and Black people that have spurred protests and renewed public discussion about police brutality.

In most cases, the officers have been white, but all five officers accused in Nichols’ death are Black. Tadarrius Bean, Demetrius Haley, Desmond Mills Jr., Emmitt Martin III and Justin Smith are charged with second-degree murder in Nichols’ death. They have pleaded not guilty.

The lawsuit names as defendants the city of Memphis, Police Director Davis, the five officers who have been fired and charged, another officer who has been fired but not charged, and an additional officer who retired before he could be fired. It also names three Memphis Fire Department employees who were fired after officials said they failed to render aid to Nichols.

The three officers who initiated the traffic stop claimed Nichols was driving recklessly the evening of Jan. 7. However, the lawsuit said they stopped him for reasons that have “never been substantiated.” Davis has said that she has seen no evidence justifying the traffic stop or the officers’ response.

Before stopping Nichols, Martin called into dispatch to run his license plate for warrants or traffic infractions, and the response came back negative, the lawsuit states. Nonetheless, the officers boxed Nichols’ car in while he was stopped at a red light.

Martin and Haley deactivated their body worn cameras, the lawsuit states. They ran to Nichols’ car and pulled him out without explanation. They wore black sweatshirts with the hoods pulled up and did not identify themselves as police. Hemphill, meanwhile, “sprinted out of his unmarked squad with his gun drawn, held sideways, and pointed squarely at Tyre—ready to deploy deadly force on a non-resistant individual for an unknown and unidentified offense.”

“What did I do?” Nichols asked during the encounter, the lawsuit said.

The officers pinned him to the ground and pepper-sprayed him while threatening to break his arm and fire a stun gun at him. When Nichols managed to run away, Hemphill did fire his stun gun, according to police records.

Nichols was captured a few minutes later by Mills, Bean and Smith. Joined by Haley and Martin, they brutally punched, kicked, and pepper-sprayed him and beat him with a baton for seven minutes straight, all while he was physically restrained, according to the lawsuit.

Just feet from his home, Nichols was beaten so badly that he was “left unrecognizable,” the lawsuit states, comparing his case to that of Emmett Till some 70 years prior and the officers to a “modern-day lynch mob.”

“Unlike Till, this lynching was carried out by those adorned in department sweatshirts and vests and their actions were sanctioned—expressly and implicitly—by the City of Memphis,” it said.

The officers’ own body cameras recorded them beating Nichols and then ignoring him for nearly half an hour as he was handcuffed, badly injured and struggled to stay upright while propped sitting against an unmarked police car.

The lawsuit provides new details of the trauma Nichols suffered. He arrived at the hospital with no pulse, it states, and had suffered cardiac arrest. He was intubated and put on dialysis because his kidneys were failing. His face was so swollen as to be unrecognizable. He had broken teeth. His brain was swollen and unable to function properly.

Mills’ lawyer in the criminal case said Mills would be hiring a different lawyer to represent him in the civil case. Hemphill’s lawyer declined immediate comment. Martin’s lawyer said he had not yet seen the lawsuit and did not immediately comment. Lawyers for Bean, Haley and Smith did not immediately respond to requests for comment.

The suit says that the city of Memphis hired Davis as police chief knowing that she had played a prominent role with a specialized police unit in Atlanta that was eventually disbanded after allegations of excessive force.

The lawsuit accuses Davis of forming an identical unit in Memphis that “predictably implemented the same unconstitutional mandates, policies, and customs” It accuses Davis and other police supervisors of encouraging officers to engage in illegal searches and seizures.

The lawsuit accuses the police department of lowering standards for who could become an officer and making it easier to graduate from the police academy by allowing recruits to retake exams several times at the time the officers involved in Nichols’ beating were brought on. In addition to being less qualified, new recruits were not properly trained in a number of areas, including probable cause, traffic stops, the Fourth Amendment, and use of force, it said.

The lawsuit comes more than a month after the Justice Department announced that it will review the police department’s policies on the use of force, de-escalation strategies and specialized units in response to Nichols’ beating.

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Loller contributed from Nashville, Tenn. AP reporter Rebecca Reynolds contributed from Louisville, Ky.