A Cleveland police officer was acquitted for his role in the 2012 fatal shooting of two unarmed people in a car after officers mistook the sound of the car backfiring as gunshots.

After a four-week trial, a judge found officer Michael Brelo, 31, not guilty of two counts of felony voluntary manslaughter in the deaths of Timothy Russell, 43, and Malissa Williams, 30. Russell and Williams were killed Nov. 29, 2012, after they led 62 police vehicles on a chase across Cleveland.

"The state did not prove beyond a reasonable doubt that the defendant Michael Brelo knowingly caused the deaths of Timothy Russell and Malissa Williams," said Judge John O'Donnell in his ruling, "because the essential element of causation was not proved for both counts."

In Cleveland, city leaders braced for protests and called for calm. The verdict comes at a time of growing national scrutiny of the use of force by law enforcement against people, especially minorities. Brelo is white and the two victims were black.

Brelo, a seven-year veteran, is the first of six Cleveland officers to be prosecuted in the 2012 fatal shooting of Russell and Williams. Five police supervisors — none of whom fired shots — also each face misdemeanor counts for "dereliction of duty." No trial date has been set.

When Russell's Chevy Malibu finally came to a stop in East Cleveland, 13 officers opened fire, shooting at least 137 rounds into the vehicle. Brelo, prosecutors said, was the only one who continued to shoot after the threat was over. He climbed onto the hood of the Malibu and shot 15 rounds into the windshield, striking Russell, who was driving, and Williams, who was in the passenger seat.

O'Donnell spent nearly 50 minutes explaining his decision. He walked through the conflicting forensic testimony, using two mannequins in the courtroom to show the trajectory and location of gunshot wounds to the victims. Ultimately, the judge said multiple officers fired shots that could have been fatal to Williams and Russell.

The judge said that officers acted reasonably based upon radio traffic that officers were being fired upon.

"It is Brelo's perception of a threat that matters," O'Donnell said in court. "Brelo was acting in conditions difficult for even experienced police officers to imagine."

Brelo, who has been suspended without pay, did not testify.

Immediately after the judge's verdict, Brelo put his head in his hands in tears, while several local activists watching in an overflow room began to chant "No Justice, No Peace."

The case hinged on whether the fatal shots were fired by Brelo or one of the other 12 officers. The judge heard from forensic pathologists, siblings of the victims, ballistics experts, a forensic mechanic, use-of-force experts and police officers.

"We are elated," said Patrick D'Angelo, one of Brelo's attorneys, who declared that the prosecutor was a bully. "This has been a bloodfight, tooth and nail."

Steve Loomis, who heads the Cleveland Patrolman's Union, slammed the prosecution, declaring that it had unfairly targeted his officers - many of whom did not cooperate with the investigation.

Cuyahoga County Prosecutor Timothy McGinty said he was "profoundly disappointed" with the verdict.

"The trial forced us to examine how and why so many errors and flawed assumptions could have led to the deaths of two unarmed people," McGinty said.

He noted additional officers still face their day in court on lesser charges in the fatal shootings. And, he said a Department of Justice Investigation prompted by the case will lead to reforms.

The Justice Department began investigating Cleveland police in March 2013 following a string of "highly-publicized" use-of-force incidents. The investigation ended in 2014, concluding that the department "engages in a pattern or practice of using excessive force." Officials with Justice and Cleveland are working to develop reforms overseen by a monitor.

After the judge's verdict, the Civil Rights Division at Justice, the FBI and the U.S. Attorney's office issued a joint statement that said they would review testimony and evidence from the trial and "collaboratively determine what, if any, additional steps are available and appropriate." That review is independent, the statement said, of the federal pattern and practice investigation.

After the ruling, deputies who had been guarding the 18th-floor courtroom rushed to the ground floor, where several dozen protesters were gathered.

Overcome with emotion, Renee Robinson, who said she was a cousin of Williams, sobbed uncontrollably as a crowd of demonstrators stood around her.

"Why? Why? Why?!" she said. "My cousin, from my family, she's never coming back. And now that officer gets to go back to his family. Like nothing happened."

Cleveland Mayor Frank Jackson called for calm. Hours later, more than 100 people gathered for a peaceful demonstration marking the 6-month anniversary of the shooting of 12-year-old Tamir Rice by Cleveland police.

Six months ago a white police officer shot and killed Rice, who was black, while he was playing with a toy gun in a park near his home. County investigators are finalizing their investigation for prosecutors. A spokesman for prosecutors said they will present the evidence to a grand jury.

In recent weeks, other high-profile cases involving the deaths of people at the hands of police have emerged. Six Baltimore officers were indicted May 1 for the murder of Freddie Gray, a black man who died after a spinal injury following an arrest. And, on April 7, South Carolina authorities charged Michael Slager, a white officer, with murder for fatally shooting a black man as he fled a traffic stop.

Prosecutions of officers for the use of deadly force are rare given there have been thousands of fatal police shootings in the past decade. When criminal charges have been pursued, officers have most often been acquitted or cleared, according to a recent analysis by The Washington Post in conjunction with criminologist Philip Stinson and researchers at Bowling Green State University.

From 2005 through early April, 54 officers have been charged criminally for shooting and killing someone in the line of duty, the analysis found. Of the 35 cases that had been resolved, 21 officers were acquitted or saw their charges dropped, 11 cases resulted in convictions, and in three cases the officers entered guilty pleas and were placed on probation. Brelo is the second officer in Ohio to face charges in a decade. The other officer also was acquitted.

The fatal shooting in 2012 of Russell and Williams in East Cleveland was the outcome of a chain of events that began shortly before 10:30 p.m. when an officer in an unmarked car activated his windshield strobe lights and attempted to stop the 1979 Chevy Malibu for a turn-signal violation. The blue Malibu, driven by Russell, stopped but drove off as the officer got out of his car.

About five minutes later, the Malibu that Russell was driving backfired as it drove past police headquarters. Officers mistook the sound for gunfire and began to pursue it. A forensic mechanic testified in court that a hole in the muffler indicated the car had a history of backfiring.

"Old Chevy, on St. Clair just popped a round," one officer radioed at 10:33 p.m. according to a transcript of radio traffic later introduced as evidence at trial. The radio transmission set off what became a 20-mile chase involving more than one-third of the 276 officers on duty with the Cleveland Police Department that night, according to prosecutors.

During the chase, some officers reported that someone was shooting at them from the window of the Malibu. At least one officer reported that was not the case and at 10:47 p.m. radioed: "Passenger just put his hands out asking us to stop. He does not have a gun. He has black gloves on," the officer said, according to the transcript.

"There's a red pop can in his hand."

That didn't stop the pursuit. Seconds later, the Malibu dead-ended into a middle school parking lot and was rammed by an officer's car. The car spun to a halt as officers began to open fire.

Brelo fired his Glock 17 from the driver's seat of his car, reloaded and emptied a second 17-round magazine, according to the investigation. He exited his patrol car, according to testimony, to get to a safer position behind another squad car, according to court documents.

A state investigator who interviewed Brelo following the incident testified that Brelo said that he drew on his Marine training to "go to an elevated position and push through the target."

Brelo stepped onto the hood of the Malibu, where he fired 15 shots into the windshield, prosecutors said.

Brelo had told state investigators that he did not recall getting on the hood of the car. At trial, a state forensic scientist testified that he matched photos of footprints on the Malibu to impressions made of Brelo's boots.

When the firing ended, Brelo placed the Malibu that was still running in park and removed the keys as another officer searched the victims for a pulse and a gun. Neither was found.

The entire shooting was over in 17.8 seconds. Russell, the driver, was shot 23 times; Williams, 24. Prosecutors said that evidence showed Brelo fired 49 times.

Both Williams and Russell were homeless, mentally ill and addicted to drugs, family and officials said. Police later determined the pair were under the influence of drugs the night they were killed.

Williams and Russell met in a nursing home where Russell had been undergoing rehabilitation after a car accident in which he "tried to outrun a police car," his sister Michelle Russell said in court.

Russell, of Maple Heights, had struggled with drugs and had been diagnosed as bipolar, she testified. He was the father to an 18-year-old and a self-employed bathtub refinisher, a trade he learned after being incarcerated.

"He was really trying to get his life together," his sister testified of Russell and his struggle with drugs. "He would walk past the church, often ask the church members to pray for him that he could overcome, you know, that situation because he wanted to overcome that."

Williams, of Garfield Heights, was a sweet girl, said her uncle, Walter Jackson Sr. He said he and his mother helped raise Williams after her mother abandoned her as a child. As she grew older she got involved with drugs and was diagnosed with schizophrenia, Jackson said.

Eventually, after repeated bouts with the law, she was imprisoned at a women's correctional facility in Ohio alongside her mother, he said.

Jackson called his niece's killing a "black eye" for the city. "Everybody was acting like [expletive deleted] cowboys that night," he said.

It's been nearly two years since an officer has been convicted of shooting and killing someone in the line of duty, according to The Post analysis.