The authorities in the state of Ohio in the United States have appealed for calm after a policeman was cleared of all charges relating to the killing of an unarmed black couple in Cleveland three years ago.
The policeman who climbed on to a car bonnet and fired repeatedly through the windscreen at unarmed black occupants has been cleared of all charges.
Timothy Russell and Malissa Williams died in 2012 in a barrage of bullets fired by 13 officers in a car chase.
Michael Brelo, 31, the only officer to be charged, was cleared of voluntary manslaughter at the court in Cleveland.
The verdict prompted angry protests, which continued into the night with some arrests made.
The US has seen a series of police race-related killings, some of which have led to serious civil unrest.
In Cleveland itself, the police shooting last November of a 12-year-old black boy, Tamir Rice, as he waved a replica firearm, fuelled the national debate over police use of deadly force.
After the ruling, protesters gathered outside the cordoned-off courthouse, some chanting, "Hands up, don't shoot!"
They later marched from the courthouse to the recreation centre where Tamir Rice was shot.
Some 200 people also held a mock funeral procession in the city, carrying a black coffin and singing. Some held signs that said: "Will I be next?"
Officers made a number of arrests after the demonstrations continued into the night.
Police said that a woman had been injured in a restaurant after a brick was thrown through the window.
The case involving the deaths of Russell, 43, and Williams, 30, had sparked a department of justice inquiry that concluded Cleveland police had engaged in a pattern of excessive force and violation of civil rights.
Only Mr Brelo was charged because prosecutors said the pair in the car were no longer a threat when he climbed on to the bonnet of their car and fired 15 shots through the windscreen in 7.4 seconds.
But the judge said that as other officers had fired in a 137-shot barrage, he could not rule beyond reasonable doubt that Mr Brelo was responsible for the deaths.
Cuyahoga County Common Pleas Judge John O'Donnell also cleared Mr Brelo of the lesser count of felonious assault.
The judge said he would not "sacrifice" Mr Brelo if the evidence did not warrant conviction.
County prosecutor Timothy McGinty said he was "profoundly disappointed" with the verdict.
Russell's sister, Michele, said Mr Brelo would not "dodge this just because he was acquitted. God will have the final say."
Mr Brelo had faced up to 22 years in jail if convicted of voluntary manslaughter.
The incident occurred when the car, a Chevy Malibu, backfired while speeding past Cleveland police HQ, and officers thought a gun had been discharged.
Some 62 police cars were then involved in a 22-mile chase at speeds up to 100 mph.
Mr Brelo's lawyer, Patrick D'Angelo, said his client had risked his life during the chase and that the prosecution of the case was "vicious and unprofessional".
There have been a number of deaths at the hands of police in the US that have sparked race-related protests.
The two most serious were in Ferguson, Missouri, and in Baltimore.
In April, Freddie Gray died in hospital a week after Baltimore police had taken him into custody.
His death sparked weeks of protests and later riots and looting in the city.
In Ferguson, teenager Michael Brown was killed last August by a white police officer. Protests followed, and there was further unrest after a grand jury decided not to charge the officer.