Edward Nero cleared for death of Gray, an African American, who sustained fatal injuries while in police custody.
A judge has acquitted the highest-ranking officer involved in the April 2015 death of a black detainee, Freddie Gray, in Baltimore, the largest city in the US state of Maryland.
The judge on Monday acquitted Baltimore police Lieutenant Brian Rice of involuntary manslaughter, reckless endangerment and misconduct in office for the death of Gray, who was 25 when he was killed.
Baltimore City Circuit Court Judge Barry Williams handed down his verdict after a bench trial.
Rice, 42, is the highest-ranking officer charged in Gray’s death from a broken neck suffered in a police transport van.
Monday’s verdict is the latest setback for prosecutors, who have failed to secure a conviction in the trials of four officers thus far.
Rice, who is white, ordered two officers on bicycles to chase Gray, 25, when the police claimed he fled.
Gray’s death triggered protests and rioting in the city, which has a majority of black Americans, and stoked a national debate about police brutality against minorities.
Prosecutors said Rice was negligent in shackling Gray’s legs and not securing him in a seat belt, as required by department protocol.
But defence lawyers said Rice was allowed leeway on whether to get inside a van to secure a prisoner. The officer made a correct decision in a few seconds while Gray was being combative and a hostile crowd was looking on, they said.
Williams, who heard the case without a jury at Rice’s request, said prosecutors failed to show the lieutenant was aware of a departmental policy requiring seat belts for prisoners during transport.
“The state did not prove the defendant was aware of the new policy,” the judge said in court.
A handful of protesters were at the courthouse for the verdict’s announcement.
Williams previously acquitted officers Edward Nero and Caesar Goodson Jr, the van’s driver. A third officer, William Porter, faces a retrial after a jury deadlocked.
Anti-police brutality protests were renewed earlier this month when officers killed African American men in Minnesota and Louisiana, sparking at least two apparent “revenge” attacks on police.
On Sunday, three police officers were fatally shot and three others injured in Louisiana’s Baton Rouge.
Baton Rouge became the scene of large protests against police brutality after white officers shot dead 37-year-old Alton Sterling on July 5.
Police officers killed Sterling outside a supermarket, claiming he had a gun. The father of five, whose funeral was held on Friday, had been selling CDs.
Footage of the moment Sterling was killed was captured on a mobile phone and circulated online.
Sterling’s killing was followed the next day with another police shooting. An officer killed a 32-year-old black man, Philando Castile, at a traffic stop in the midwestern state of Minnesota. The aftermath of the shooting was also captured on video and streamed live by Castile’s girlfriend on Facebook.
On July 7, five white police officers were shot dead at one such protest in Dallas, Texas.
The Black Lives Matter movement – which campaigns against police killings of African Americans – disavowed the killing of the officers and said in a statement it stands for “dignity, justice and respect”.
The Guardian has documented at least 587 people killed by police across the US so far this year. From that total, 145 – nearly 25 percent – were black, although black Americans constitute only around 13 percent of the country’s total population.