CLEVELAND (AP) — A white Cleveland patrolman who participated in a 137-bullet shooting that left two unarmed black people dead in their car was acquitted of criminal charges on Saturday, leading to angry but peaceful protests.

The acquittal of officer Michael Brelo followed a determination by the U.S. Department of Justice that the police department had a history of using excessive force and violating people's civil rights. It also came at a time of nationwide tension between police and black communities highlighted by sometimes violent protests and rioting over the deaths of black people at the hands of white officers.

Here's a look at what has exacerbated the strain between the Cleveland Police Department and minority communities and what's being done about it:

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WHAT HAPPENED IN THE CLEVELAND OFFICER'S CASE?

Brelo was charged with voluntary manslaughter in the fatal shootings of driver Timothy Russell and passenger Malissa Williams on Nov. 29, 2012, after a high-speed chase 22 miles long. The pursuit began when Russell's car backfired as he sped past police headquarters and observers thought someone had fired a gun. The chase involved 62 marked and unmarked cars and reached speeds of 100 mph.

Thirteen officers fired at the car in a school parking lot that night. Only Brelo, who fired 49 shots, was charged criminally because prosecutors said he fired his final 15 shots down through the windshield while standing on the car's hood after it had stopped and because Russell and Williams no longer were a threat to officers' lives.

Brelo's attorneys argued that other officers fired during his final volley and their shots could have been fatal.

At a bench trial, the judge said he couldn't determine whether Brelo alone fired the fatal shots.

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HOW TROUBLED HAS THE CLEVELAND POLICE DEPARTMENT BEEN?

Cleveland's police have been maligned for years, most recently for the 137-bullet shooting and for the killing of a 12-year-old black boy, Tamir Rice, who had been playing in a park with a realistic-looking pellet gun.

The Department of Justice slammed the police in a report in December, outlining a string of excessive force and civil rights violations. Then-Attorney General Eric Holder announced that a lengthy investigation concluded officers unnecessarily fired their guns, hit suspects in the head with their weapons and used stun guns on handcuffed people.

The city and the Department of Justice are negotiating a consent decree aimed at reforming the police department.

Residents' discontent with police has gone beyond allegations of excessive force, though. Six years ago, the police department came under criticism following the discovery of 11 women's bodies in a home where the stench of death hung over a poverty-stricken neighborhood for months. The victims' families accused police of failing to properly investigate the disappearances because most of the women were poor drug addicts.

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WHAT'S NEXT

The Department of Justice, U.S. attorney's office and the FBI will review the testimony and evidence in Brelo's case and examine all available legal options, said Vanita Gupta, head of the Department of Justice's Civil Rights Division.

An activist, Carol Steiner, called the Brelo acquittal "a very bad precedent for Cleveland" with a decision still to come in Tamir's case.

"Police murder people of color and not have to serve one day in jail," she said.

A sheriff announced this month that the investigation into the police shooting of Tamir in November was nearly complete. Cuyahoga County Sheriff Clifford Pinkney said May 12 that investigators still had a few more witnesses to interview. He said the completed investigation would be turned over to the county prosecutor.

The fatal shooting on Nov. 22 drew national attention when the city released footage from a surveillance camera showing rookie patrolman Timothy Loehmann shooting Tamir within two seconds of a police cruiser stopping near him. Loehmann and his partner, Frank Garmback, were responding to a 911 call about a man waving a gun.

The officers remain on restricted duty. A police union official has said the officers had no way of knowing Tamir, who had an airsoft-type gun that shoots non-lethal plastic pellets, wasn't carrying a real firearm.

An attorney for Tamir's family, Walter Madison, says he can't understand why the investigation has taken so long. He says the only outcome that serves justice is criminal charges.

He and other attorneys have sued the city and the officers in federal court. The city asked that proceedings in the civil case be delayed until after the sheriff's investigation is finished.