A police officer responding to a shooting in a Chicago-area bar shot and killed a black security guard who had subdued and disarmed the shooter.

On Sunday at 4 a.m. a group of drunken men were asked to leave Manny's Blue Room Bar, witnesses told local news station WGN9.

Afterwards, someone from the group returned with a gun and opened fire.

Security returned fire, witnesses told WGN9, and an armed security guard, Jemel Roberson, apprehended one of the men involved outside.

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"He had somebody on the ground with his knee in his back, with his gun in his back like, 'Don’t move,'" witness Adam Harris told WGNTV.

But an officer responding to the scene fired at Roberson and killed him.

"Everybody was screaming out 'Security!' He was a security guard," Harris said.

The Midlothian police department confirmed to The Hill that two of its officers responded to the shooting and one opened fire.

"Upon arrival Officers learned there were several gunshot victims inside the bar. A Midlothian Officer encountered a subject with a gun and was involved in an Officer involved shooting. The subject the Officer shot was later pronounced deceased at an area hospital," Chief Daniel Delaney of the Midlothian Police Department said in a statement.

Delaney added an investigation into the shooting of the security guard is now taking place.

Friends of Roberson told the news station that he planned to become a police officer and was an upstanding man.

The Cook County Sheriff's Office will manage the investigation into the shooting at the bar as the State Police Public Integrity Task Force is investigating the shooting of Roberson.

-- Updated at 1:57 p.m.