Trenton, NJ, Police Under Investigation by Justice Dept.

The United States Justice Department began a civil rights investigation on Tuesday into the city of Trenton, N.J., and its police department after getting “serious and credible” reports of officers using improper levels of force and illegally stopping and searching pedestrians and drivers.

The inquiry into New Jersey’s capital city and its police force is expected to take a year and could lead to federal oversight of the department through a consent decree.

The review will include on-the-job observation of police officers, interviews with residents and an analysis of police records, including footage from body-worn cameras and internal affairs investigations, officials said.

Since 2021, the Justice Department has opened similar inquiries into 10 other police agencies across the country, said Kristen Clarke, an assistant attorney general with the department’s civil rights division.

These inquiries, she said, “fuel change and transformation” of police departments.

“This investigation should send a strong message to police departments across our country regarding our firm commitment to ensuring constitutional, fair and effective policing,” Ms. Clarke said.

Trenton’s mayor, Reed Gusciora, said the city would cooperate fully with the inquiry.

“The majority of our cops get up every day and do the right thing,” Mr. Gusciora said of the 260-member department.

“I’m a great believer in, ‘Let the chips fall where they may,’” he added. “I just hope that this does not affect police morale. It’s one thing to try to train officers better and another thing to disparage an entire department.”

Trenton, a city of 90,000 people on the state’s western border with Pennsylvania, has grappled for decades with high rates of crime, underperforming schools and poverty. Nearly 30 percent of city residents live in poverty, and state-owned government office buildings fill more than half of its land.

There have been 24 killings in the city this year, Mr. Gusciora said, a rate that reflects an improvement over the 40 murders reported in 2022. The city, he said, struggles with gun violence and had not fully rebounded from state cutbacks in 2011 that resulted in 125 police officers being laid off.

“It’s really tough to be a cop these days,” Mr. Gusciora said. “And it’s hard to recruit.”

Philip R. Sellinger, the U.S. attorney for New Jersey, said he participated in a community meeting last month at a church in Trenton and later got a note from a resident stating, “We’re scared of the law because they don’t like us.”

Mr. Sellinger said there was no single incident that prompted the Justice Department inquiry. But the community meeting, he said, was particularly “impactful.”

He said his office was aware of reports of police officers using significant force on drivers who were obeying instructions and on people in the throes of mental health crises.

“At times these uses of force caused very serious injuries,” Mr. Sellinger said during a news conference announcing the federal investigation.

Residents also reported that Trenton police officers “routinely conduct stops and searches without any justifiable reason,” he said.

“No warrant or probable cause — just a stop and search. Oftentimes of minority residents,” he added.

At the city’s 100-acre Cadwalader Park on Tuesday, several residents said they had never had sour interactions with city police, nor had they witnessed any potentially criminal law-enforcement tactics.

“I respect who they are and don’t involve myself in bad situations,” said James Page, a 63-year-old retired construction worker.

But his 54-year-old brother, Calvin Page, said that when he drives by some traffic stops, his head fills with questions.

“Seems sometimes they’re going overboard,” said Calvin Page, a hospital technician. “They’re pulling guys out of the car, and now they’re searching the car and the trunk — don’t you need a warrant for that?”

The office of the New Jersey attorney general, Matthew J. Platkin, who is responsible for all of the state’s police and prosecutors’ offices, did not respond to requests for comment about the Justice Department’s decision to investigate.

Sarah Fajardo, policy director of the American Civil Liberties Union of New Jersey, said residents of Trenton have for years documented “consistent and grave abuses of power.”

She said she hoped the inquiry would “bring a renewed focus on the need for increased transparency and accountability in policing across the state.”

This is not the first time that Mr. Sellinger’s office and the Trenton Police Department have debated the use of excessive force by officers.

In a federal trial in May, prosecutors from Mr. Sellinger’s office accused two Trenton police officers of using excessive force during a 2017 arrest of a man who was stopped for running a red light, but fled. One of the officers, in an interview with NJ Advance Media, insisted that he had complied with use-of-force policies established by the state attorney general’s office. He said he had refused several offers by the government to avoid trial by accepting a plea agreement.

Neither officer was convicted.

Jurors found the officer interviewed by Advance Media not guilty after the five-day trial. A partial conviction against the second officer was overturned last month after the court found evidence of prosecutorial misconduct.

Days later, a lawyer who represented the officer acquitted after the finding of prosecutorial misconduct billed the city of Trenton for $168,000 in legal fees.

Mr. Sellinger’s office then challenged the finding of prosecutorial misconduct — and won.