John Bacon, and Melanie Eversley

USA TODAY

A Maryland judge acquitted Baltimore police officer Edward Nero of all charges Monday in the controversial case of Freddie Gray, whose death last year touched off sometimes violent protests in the city and reignited Black Lives Matter demonstrations across the nation.

Nero, who is white, was the second of six officers to face trial and the first to obtain a verdict. The first case ended in a hung jury and will be retried.

Gray, 25, suffered a spinal injury while in police custody April 12, 2015, and died a week later. Prosecutors say he suffered the injury while traveling, handcuffed and without a secured seat belt, in the back of a police van after his arrest.

Nero, 30, had declined a jury trial, and Judge Barry Williams heard testimony that wrapped up last week. Nero was found not guilty of assault, misconduct in office and reckless endangerment. In issuing his ruling, Williams said prosecutors had not proved their case.

"The court is not satisfied that the state has shown that the defendants had a duty to seat belt Mr. Gray and, if there was a duty, that the defendant was aware of the duty," Williams said. "This court finds that the state has failed to meet its burden to show that the defendant corruptly failed to do an act required."

Baltimore Mayor Stephanie Rawlings-Blake issued a statement immediately after the verdict was announced asking for calm.

"Officer Nero will face an administrative review by the Police Department," she said. "In the case of any disturbance in the city, we are prepared to respond. We will protect our neighborhoods, our businesses and the people of our city."

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The Baltimore Police Department issued a statement saying the internal investigation was being handled by other departments and wouldn't be completed until all six criminal cases have been resolved.

Nero, who is white, was among a group of bicycle officers who initially pursued and helped arrest Gray, although Nero claims he did not touch Gray except to help him stand after he was handcuffed.

The case touched on national sensitivities about strained relations between law enforcement in America and community residents -- particularly black males.

U.S. Sen. Ben Cardin, a Democrat who was born and grew up in the city of Baltimore, said that while the case is sensitive, the verdict must be respected.

“No verdict will bring back Freddie Gray to his family and his community but we must ensure we continue the dialogue and the hard work to rebuild the trust between law enforcement and the neighborhoods they are sworn to protect and defend,” Cardin said.

But leaders of civil rights organizations took on a more emotional tone, expressing disbelief and disappointment at Monday's decision.

“This injustice sends a clear message to black communities that we cannot rely on law enforcement to protect our lives or the justice system to protect us from police violence,” said Rashad Robinson, executive director of Color of Change. “If police departments and our justice system want to strengthen their relationships with black communities, it is paramount for them to demonstrate that they can – and will – police their own," Robinson said.

Jumaane Williams, deputy leader of the New York City Council and cochair of the city’s Gun Violence Task Force, said there is “no question” that Nero’s decisions led to Gray’s death.

“I continue to be angered, frustrated and disappointed about the message these decisions send and the implications they give about the value of black lives in America,” Williams said. “I will be following the cases of the other officers involved in Gray’s death closely. It’s my sincere hope that there will be accountability.”

The NAACP national office, which is based in Baltimore, released a statement saying the organization would continue to wait for justice for Gray.

"We respect the legal process and pray that the family of Freddie Gray will receive justice for his tragic death as we continue to call on systemic reforms in municipal and state police department across the country," the statement read.

Nero was accused in connection with the initial arrest — prosecutors say there was no probable cause — and with later failing to properly secure Gray in a police van. Nero's lawyers claim he had little to do with the arrest and it was the responsibility of the officers in the van to buckle Gray.

Nero was the second officer to stand trial in the case. The trial of officer William Porter ended in a hung jury, and Porter, who is black, faces retrial later this year. The other officers, two black and two white, also face trials in the coming months.

Maryland lawyer Tim Maloney, who has represented — and sued — numerous police officers, said convicting Nero for misconduct on grounds there was no probable cause for the arrest would have set a dangerous precedent.

"That would mean that every officer who makes an arrest could face this (charge)," Maloney, who is not involved in any of the Freddie Gray cases, told USA TODAY.

Nero's decision to have a bench trial could be repeated by the other officers, Maloney added. "A jury can be swayed more by emotion than by law," he said.

In Baltimore, Gray's death sparked riots that tore the city apart, was blamed for an increase in violent crime and led to the dismissal of police chief Anthony Batts. The city agreed in September to pay Gray's family $6.4 million to settle civil litigation in the case.