CHICAGO » A judge’s surprise acquittal of an off-duty Chicago police officer in the shooting death of an unarmed woman called into question prosecutors’ decision not to charge the man with murder, and set off protests outside the courthouse and near the site of the killing.

That the officer shot Rekia Boyd, 22, was never in dispute. But the judge said he was bound to find detective Dante Servin not guilty of involuntary manslaughter — because manslaughter requires evidence of "recklessness," while the judge described the act of shooting as "intentional."

"It is intentional and the crime, if any there be, is first-degree murder," Judge Dennis Porter said in his seven-page ruling.

Carrying signs saying "Black Lives Matter" and "Avenge Rekia," dozens of people rallied Monday night at a park on the city’s West Side to protest the verdict hours earlier. Tying the slaying to other, more recent police shootings like the one last year in Ferguson, Missouri, protesters called on Chicago to "stand up."

"We’ve got to make it clear that we don’t even care what the legal system said. The streets say, ‘Guilty,’" said protester Jedidiah Brown. "The streets will not rest with this verdict the way it is."

Boyd was walking to a store with three friends in March 2012 when Servin, upset over noise, asked them to quiet down. Servin says he fired because he believed another person in the group was moving toward him with a gun, though police found only a cellphone.

Prosecutors say he fired five shots over his shoulder from inside his car at the group, who all had their backs to him in an alley. Boyd was struck in the head and one other person was grazed by a bullet.

The city settled a wrongful-death lawsuit with Boyd’s family for $4.5 million in 2013. A few months later, the Cook County state’s attorney’s office charged Servin with involuntary manslaughter.

But after a four-day bench trial, Porter ruled that prosecutors failed to prove Servin acted recklessly, in the precise legal sense of the word. He said that Illinois courts have consistently held that the act of pointing a gun and firing is an intentional act, not a reckless one.

Cook County State’s Attorney Anita Alvarez disagreed and said in a statement that she was "extremely disappointed."

"The state’s attorney’s office brought charges in this case in good faith and only after a very careful legal analysis of the evidence as well as the specific circumstances of this crime," Alvarez said.

Boyd’s brother, Martinez Sutton, erupted in anger inside the courtroom after hearing the verdict, shouting, "This (expletive) killed my sister." Relatives of the slain woman chased after Servin and called him a murderer as a he left the courthouse under the escort of several supporters.

"With somebody laying in an alley with a bullet hole in her head, how is that not guilty?" asked Boyd’s sister, Natasha Sutton.

Servin told reporters he had no regrets, though he said his "heart goes out to the family."

"Any police officer, especially, would have reacted in the exact same manner that I reacted, and I’m glad to be alive. I saved my life that night," Servin said.