The officer is 42-year-old Gerald Callahan and he has been relieved of his police powers while his actions are investigated.
Despite being off-duty this officer was armed with his Smith and Wesson but it remained holstered during the brawl. Witnesses say he did enough damage with his two fists.
It has also come to light that some believed this officer should have been fired from the force long ago.
It was closing time. Just after two o'clock Saturday morning at a Niles restaurant and lounge. Employees say Officer Gerald Callahan was saddled up to the bar for less than two hours. They claim he only had two drinks and for the most part kept to himself.
A Niles Police Department press release says there's evidence "Callahan attacked the two victims for no apparent reason." Witnesses say they were stunned.
One second a 61-year-old man and his date were chatting with each other at the bar... the next, the off-duty officer who was sitting a seat away suddenly sprang-up and starting throwing punches.
"No words were exchanged," said a witness who asked not to be identified, "he just started pounding the guy over and over."
When it was over, Niles Police say the 61-year-old victim suffered "lacerations and bruises to his head and face." His 50-year-old female companion had "lacerations on her arm and lip."
Witnesses say the burly cop cut and ran when local police were called.
Niles officers say they found Gerald Callahan passed-out in some bushes about a block from the bar.
They brought him to the local station house where they discovered Mr. Callahan was a Chicago cop. Niles Police informed Callahan's bosses at Area 4 police headquarters on the near West Side.
A source says several members of the command team rushed out to Niles.
Mr. Callahan was charged with two counts of battery and released on bond. But this isn't the first time he's run afoul of the rules. In 2006 former Chicago Police Superintendent Phil Cline recommended Callahan be fired after he was accused of threatening his fellow officers.
A newspaper report at the time says the threats allegedly included a vow to dump a few of his fellow officers in a garbage can and rip one officer's "f---ing head off."
It's unclear why the Chicago police board decided to keep Mr. Callahan on the force.
Attempts to reach them and officer Callahan were unsuccessful Saturday night.
A Chicago police spokesperson will only say the entire incident is under review and officer Callahan has been relieved of his police powers.
It's worth mentioning this all happened at a pretty nice restaurant and lounge, we're told in the dozen years it's been open, this is its first fight.