A judge's verdict clearing an off-duty Chicago Police detective in the shooting death of 22-year-old Rekia Boyd was "unusual, not rare," according to an expert on Illinois criminal law.

Monday's ruling, by Judge Dennis Porter, cleared Chicago Police Det. Dante Servin on charges of involuntary manslaughter, reckless discharge of a firearm and reckless conduct when he shot and killed Boyd near Douglas Park three years ago. "It sounds like what Judge Porter did was come to the conclusion that … even if you take all the evidence in favor of the state, they haven't proven what they need to," said Professor Richard Kling of the Illinois Institute of Technology's Chicago-Kent College of Law.