Baltimore police officer Caesar Goodson Jr has been found not guilty of all criminal charges including second-degree depraved heart murder in the case of black detainee Freddie Gray, who died from injuries sustained while in police custody.
Judge Barry Williams handed down the verdict in Baltimore City Circuit Court on Thursday.
Goodson, 46, was the driver of a police transport van in which Gray broke his neck in April 2015. His death triggered rioting and protests in the majority black city.
Goodson had also faced three counts of manslaughter, and single counts of reckless endangerment, second-degree assault and misconduct in office.
Goodson, who is also black, faced the most serious charges among the six officers charged in Gray's death, making his the marquee case for prosecutors.
They failed to secure a conviction in two earlier trials of officers.
"This court is satisfied the state has failed to show" evidence of the crimes, Williams said.
Prosecutors contended Goodson gave Gray a "rough ride", failed to ensure his safety and should have called a medic.
"That is an inflammatory term ... that when uttered is not to be taken lightly," said Williams.
Goodson's defence team argued that Gray caused his own injuries by falling inside the transport van. Goodson also lacked the training to recognise that Gray was hurt, they said.
Goodson waived a jury trial, leaving it to Williams to decide his fate.
Gray's death spawned protests, rioting and arson in the majority African-American city of 620,000 people and stoked a debate on US police treatment of people of colour.
Gray, 25, was arrested after fleeing police officers in a high-crime area. He was bundled into Goodson's van shackled and not secured with a seat belt inside the van, a violation of police procedure.
Several dozen protesters gathered outside the courthouse, chanting "Justice for Freddie Gray".