Judge Diane Cannon played up inconsistencies in Rickey Williams' account of the on-duty incident, saying his testimony at the trial last week "taxes the gullibility of the credulous."
The recent Evans-Williams case attracted public and media attention, as reports of police brutality in the US have risen dramatically recently and numerous high-profile cases have prompted protest marches around the country.
The new ruling is thought to spark additional protests since justice was clearly not served on Monday.
Cook County Judge Diane Cannon delivered a judgment in favor of Cmdr. Glenn Evans, 53, who was accused of two counts of aggravated battery and seven counts of official misconduct.
‘Law and order' was finally handed down two years after Evans allegedly shoved his gun in the mouth of 25-year old Ricky Williams and pressed a stun gun against him.
According to the judge, William's testimony was not acceptable because the suspect could not pick Evans out in a lineup.
"His testimony taxes the gullibility of the credulous," Cannon said, adding that Williams was "eager to change his testimony at anyone's request to accommodate the evidence."
African-American police commander Evans, working in the Chicago police force for 29 years, could have been imprisoned for up to 5 years.
Prosecutors claim that DNA found on Evans' weapon showed that he shoved the gun in William's mouth. Cannon dismissed the evidence saying that it could be simply a "touch" effect coming from Evans touching Williams and then touching his gun.
Asked why he was confronted by the police officer the 25-year old Williams suggested that the policeman must have mistaken his cellphone for a weapon. Evans confirmed his words claiming that he saw Williams holding a gun, during his testimony at the trial, Sputnik News reported.
The case comes as the Chicago Police Department is increasingly scrutinized in light of widespread accusations of racism and brutality.
Police brutality and racism is seen as endemic in the US. Evans was not suspended from duty following his charges, and it remains unclear if will be allowed to continue working as a police officer following the judgment.