Judge Dennis Porter handed down the verdict Monday afternoon amid heavy security in his courtroom, but not before asking anyone who might become emotional to leave.
"I know this case has generated a lot of emotion ... but this is a court of law, not a court of emotion," Porter said before issuing a long ruling.
Porter said while he had no doubt that Officer Dante Servin did indeed shoot Boyd, he said prosecutors didn't prove Servin acted recklessly when he did so, a requirement for finding someone guilty of manslaughter.
After the verdict was read screaming members of Boyd's family were dragged from the courtroom as Servin hugged relatives.
"You want me to be quiet?! This m----------- killed my sister!" Boyd's brother, Martinez Sutton, screamed as he was dragged out of the courtroom by deputies.
Outside the courthouse, protesters began to gather and Boyd's mother, Angela Helton, sobbed with family.
"He murdered my daughter in cold blood," Helton said.
Sutton cried as he gathered with family outside the courthouse.
"When we walked in, we already knew we lost," he said.
Servin, now 46, was off-duty when he opened fire at a group of people near Douglas Park on March 21, 2012, striking Antonio Cross in his hand and Boyd in the back of her head. Servin has said he saw Cross pull a gun, but police never recovered a weapon, and prosecutors argued Cross was holding a cellphone.
Servin faced charges of involuntary manslaughter, reckless discharge of a firearm and reckless conduct.
Servin's defense team, meanwhile, argued that Servin only began shooting after Cross lifted his cellphone and pointed it toward Servin as if it were a gun. According to testimony, Servin told authorities he thought he saw a gun, heard a bang and felt "something" hit the back of his head.