Federal authorities are launching a civil rights investigation into the state's capital city and its police department.

The Department of Justice says it's probing alleged misconduct within the Trenton police force, citing concerns that officers regularly used excessive force and routinely stopped motorists and pedestrians without justification, illegally searching their homes and cars.

In announcing the investigation, New Jersey's U.S. attorney Phil Selinger said Trenton residents have long complained about the department's alleged practices leading to the federal inquiry.

Mayor Reed Gusciora and police Director Steve Wilson say they'll cooperate.

The union representing Trenton police officers responded, citing ongoing staffing shortages since 2011.

That's when budget cuts forced the city to lay off more than 100 officers.

If the investigation reveals the department broke federal law, the DOJ can sue to force changes.