MEMPHIS, TENN. -- The U.S. Department of Justice said Thursday it is investigating the patterns or practices of the police department in Memphis, Tennessee, nearly seven months after the violent beating of Tyre Nichols by five officers after a traffic stop.

Assistant Attorney General Kristen Clarke of the Civil Rights Division made the announcement in Memphis. Federal authorities will use the investigative tool to look collectively at the Memphis Police Department's use of force and stops, searches and arrests, and whether it engages in discriminatory policing.

She said that in even in the majority Black city of Memphis, the police department may be disproportionately focusing its traffic enforcement on Black drivers.

Clarke said the probe will look into the city and its police department. She mentioned Nichols' death, but said the investigation is not based on a single event, or a single unit with the police agency. The Nichols case joined the list of problematic killings of Black people by police in recent years and intensified national calls for police reform.

"The tragic death of Tyre Nichols created enormous pain in the Memphis community and across the country," Attorney General Merrick Garland said in a news release. "The Justice Department is launching this investigation to examine serious allegations that the City of Memphis and the Memphis Police Department engage in a pattern or practice of unconstitutional conduct and discriminatory policing based on race, including a dangerously aggressive approach to traffic enforcement."

Clarke said the Department of Justice has received reports of officers escalating encounters with people in the community and using excessive force; using force punitively when they perceive someone's behavior as insolent; and using force against people who are already restrained or in custody.

Rodney Wells, Nichols' stepfather, told the Associated Press that he hopes the probe will lead to changes in the way police deal with Memphis citizens.

"We're moving in the right direction, trying to get some justice," Wells said.

Clarke said investigators will ride along with Memphis police and speak with officers as part of the probe. She said the Justice Department told the police chief and mayor about the investigation, adding that they pledged to cooperate.

However, Memphis Mayor Jim Strickland said he was "disappointed that my request was not granted by the Department of Justice to discuss this step before a decision was made to move down this path."

"I know they discussed the need for such an action with many other individuals. I hope the remainder of the process is more forthright and inclusive than it has been so far," Strickland said in an statement.

Memphis Police Director Cerelyn "CJ" Davis said officers are expected to follow their training and department policies.

"While the officers involved in the Tyre Nichols case demonstrated no regard for these tenets, I am appreciative of the MPD officers that continue to serve our city with integrity," she said.

The five officers have pleaded not guilty to criminal charges including second-degree murder in the Jan. 7 beating of Nichols after a traffic stop -- and his death three days later. Caught on police video, the beating of the 29-year-old Nichols was one in a string of violent encounters between police and Black people that sparked protests and renewed debate about police brutality and police reform in the U.S.

The five officers charged in the case are Black. So was Nichols.

The officers were part of a crime-suppression team known as Scorpion. They punched Nichols, kicked him and slugged him with a baton as he yelled for his mother. The police chief disbanded the Scorpion unit after Nichols' death.

In addition to the officers fired and charged with murder, one white officer who was involved in the initial traffic stop has been fired. That officer will not face charges. Another officer, who has not been identified, also has been fired. An additional officer retired before he could be fired.

Three Memphis Fire Department emergency medical technicians were fired for failing to render aid to Nichols. Two Shelby County Sheriff's Office deputies who went to the location after the beating were suspended for five days for policy violations.

Activists have been calling for a pattern or practice investigation into Memphis police for years stemming from several incidents, including the fatal shooting of Darrius Stewart, a Black man who was killed by a white officer during a traffic stop in 2015, and a federal court order about improper police surveillance of activists.

"This is a necessary step in ensuring the citizens of Memphis have our civil rights protected and that we moving beyond tacit political talking points regarding Criminal Justice Reform," said Memphis activist Earle Fisher.

The Memphis City Council passed an ordinance earlier this year that outlawed so-called pretextual traffic stops, which include minor violations such as a broken tail light. But some activists have complained that the ordinance has not been consistently enforced.

In June, a similar Department of Justice probe alleged that Minneapolis police systematically discriminated against racial minorities, violated constitutional rights and disregarded the safety of people in custody for years before George Floyd was killed.

And in March, the department found Louisville police engaged in a pattern of violating constitutional rights and discrimination against the Black community following an investigation prompted by the fatal police shooting of Breonna Taylor.

The investigations can take years -- both the Louisville and Minneapolis probes were launched in April 2021.

Depending on their findings, the investigations can result in agreements that require reforms that are overseen by an independent monitor and are approved by a federal judge. The federal oversight can continue for years.

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Mattise reported from Nashville.