TRENTON, N.J. − The U.S. Department of Justice has launched a federal civil rights investigation into New Jersey's capital city and its police department's use of force, stops, searches and arrests.

The "pattern or practice investigation" will determine whether the Trenton Police Department has systemically violated federal law or the Constitution. It will include a comprehensive review of the department's policies, training, supervision, internal investigation protocols, disciplinary decisions and other protocols regarding complaints, the Department of Justice said in a statement Tuesday.

"Unfortunately, we have reviewed numerous reports that Trenton police officers may have used force inappropriately and conducted stops, searches, and arrests with no good reason in violation of individuals’ constitutional rights," U.S. Attorney Philip R. Sellinger said Tuesday. "Today’s announcement reflects our office’s commitment to ensuring effective, constitutional policing in Trenton and throughout New Jersey."

In response to the probe, the unions representing police in the city and state said in a joint statement they "hope that this inquiry will also shed light on the pressing need for additional resources and support for our officers."

"On a personal level, the Trenton police for a decade have been doing impossible work with a skeleton crew that is just extraordinarily dedicated to the city without a contract, without proper working conditions," Pat Colligan, president of the New Jersey State Policemen's Benevolent Association, told USA TODAY. "So, I'd like the Department of Justice to look at the full picture and the full story before they jump to a conclusion."

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Trenton probe follows police shooting

The investigation was welcomed by Mount Laurel attorney Gregg Zeff, who represents a former Burlington City resident who was shot and paralyzed by Trenton police in February 2022.

"I'm also frustrated that it took the paralysis of Jajuan Henderson to bring this to the attention of the federal government, but it did not wake up Trenton," Zeff said.

Henderson's lawsuit contends police officers approached his parked car shortly after midnight, smashed the driver's side window and shot him as he tried to call for help on his cellphone.

But police said Henderson, then 29, was unable to produce an ID or driver's license, and that he refused to leave the vehicle after being told he was under arrest. Police also alleged Henderson reached around the vehicle's interior, "including below seats."

Assistant Attorney General Kristen Clarke, who oversees the Justice Department's civil rights division, said the investigation was not prompted by a specific incident and the department is not alleging racial discrimination.

What happens after a pattern or practice investigation?

Just one pattern and practice probe was opened during Donald Trump's presidency, but the inquiries became more common again under the Biden administration. Following the murder of George Floyd and nationwide racial justice protests, the Justice Department launched investigations into police departments in Louisiana, Kentucky and Phoenix. 

In June, Attorney General Merrick Garland announced Minneapolisand its police departmentengagedin a pattern of violating people's rights through the unnecessary, unjustified use of deadly force and discrimination following a two-year pattern or practice investigation. In July, the department launched a similar investigation into the city of Memphis and the Memphis Police Department. The investigation came more than six months after Memphis police officers brutally beat 29-year-old Tyre Nichols during a traffic stop and Nichols died three days later.

Federal officials closed 26 of the nearly 70 investigations conducted between 1994 and 2016 without finding a pattern or practice of police misconduct, according to a 2017 report from the Justice Department.

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But when such a pattern or practice is found, the investigations are often resolved with a consent decree, which require agencies meet specific goals before federal oversight is ended, according to the Justice Department. Though consent decrees have been credited with successfully improving practices in some of the country's 18,000 police departments, some officials have criticized the court-enforced plans for being expensive, time-consuming and ineffective elsewhere.

The investigation in Trenton is expected to take one year, "and if we substantiate those violations, the department will take appropriate action to remedy them," Clarke said Tuesday.

Contributing: Bart Jansen, USA TODAY; Kim Strong, Asbury Park Press;