Assistant Attorney General Thomas Perez said the investigation will look beyond the November car chase that involved more than 60 patrol cars and ended in the shootings of Timothy Russell, 43, and his 30-year-old passenger, Malissa Williams.
Perez said the probe will not be a criminal investigation; its focus is the entire department, not individual officers. It will analyze several years of excessive force claims as well as police policies, training and procedures, he said.
"We go into this with no preconceived notions," Perez said at a news conference in Cleveland.
City leaders had asked the federal government to review Cleveland police division policies after that chase, which raised questions about the conduct of officers. But Perez said there was not one tipping point that led to the wider investigation.
Cleveland Mayor Frank Jackson said he welcomed the expanded investigation. "It is vital that there is a level of trust between police and the community," he said.
Relations have been strained between Cleveland police and some community leaders since the chaotic police chase ended with 13 officers firing on the car.
Russell and Williams were each shot more than 20 times. Some officers thought they were armed, but no weapon or shell casings were found.
The chase went through residential neighborhoods and onto a freeway before ending behind a school in neighboring East Cleveland. It reached 100 mph and covered 25 miles over 22 minutes.
Ohio's attorney general conducted a separate investigation and said leadership and communications failures led to the escalation of the Nov. 29 chase. The report did not assign blame on any of the officers and concluded crossfire led some officers to believe they were in a shootout with the vehicle's occupants.
A grand jury will likely determine if any of the officers should face criminal charges.
Some community leaders called the shootings racially motivated because Russell and Williams were black.
A police union attorney has said race had nothing to do with the shooting and said it would be found to be justified because, he said, the driver of the car tried to run over several police officers and intentionally rammed other patrol cars.
U.S. Attorney Steven Dettelbach said Thursday there is a great deal of respect for the officers and department leaders.
"That does not mean there aren't areas where there might be room for improvement," he said.