A protester with his hands up walks by a Cleveland police officer following a not guilty verdict for Cleveland police officer Michael Brelo on manslaughter charges, in Cleveland, Ohio, May 23, 2015. [Photo/Agencies]

CLEVELAND - Some 71 people were arrested in Cleveland overnight during protests that flared after a police officer was found not guilty in the shooting deaths of an unarmed black man and a woman following a high-speed car chase in 2012, police said on Sunday.

Protests were mostly peaceful after the judge's verdict was announced on Saturday, Police Chief Calvin Williams said. But later in the day, some people "crossed the line," assaulting bystanders in a downtown area, briefly blocking a major highway and disrupting business at a shopping center, he told a news conference.

The unrest comes amid a national outcry over the law enforcement's use of lethal force against minority groups. Over the past year, the deaths of unarmed black men during confrontations with police in Ferguson, Missouri, New York City, Baltimore and elsewhere have spawned protests and occasional violent outbursts around the United States.

Williams said police in Cleveland "gave people the space and a safe environment" to demonstrate peacefully but said would not allow violence towards people or property.

In one incident, protesters assaulted bystanders with pepper spray in a downtown area, Williams said. Another was arrested for throwing a sign at a person entering a restaurant, as were two other protesters who tried to interfere when police moved in, Williams said.

Businesses in Tower City Center shut down for the day when protesters entered the shopping complex and became disruptive, he said.

Protesters took to the streets after Judge John O'Donnell acquitted police officer Michael Brelo, 31, on charges of voluntary manslaughter and aggravated assault in the deaths of Malissa Williams and Timothy Russell.

Malissa Williams and Russell were black and Brelo, a former Marine, is white.

The judge ruled Brelo acted reasonably in shooting the two while standing on the hood of their surrounded car and firing multiple rounds through the windshield. Brelo was one of a group of officers who fired on the car at the end of a chase that began in downtown Cleveland after reports of gunfire coming from the car.

The US Justice Department said on Saturday its civil rights division, the US attorney's office and the FBI were reviewing testimony and evidence from the state trial and would determine if federal action would be taken.

Brelo's trial came months after the Justice Department found the Cleveland Police Department systematically engages in excessive use of force against civilians.

The department, in a December report, found that supervisors tolerated and in some cases, endorsed use of unnecessary or unreasonable force.

Just days before the report was released, a Cleveland police officer shot and killed Tamir Rice, a 12-year-old boy who was carrying what turned out to be a replica gun that typically fires plastic pellets. The shooting is under investigation.

Five other police supervisors were indicted on misdemeanor dereliction of duty charges in the deaths of Williams and Russell and are scheduled to go on trial in July.

Dozens of officers have been disciplined and Cleveland paid the families of Williams and Russell $1.5 million each to settle a wrongful death lawsuit. Brelo will remain on unpaid suspension until a police review is completed, police chief Williams said.