A police officer shot and killed an armed security guard while responding to a shooting at a suburban Chicago bar early Sunday, a federal lawsuit says.

Jemel Roberson, 26, died following the shooting at Manny’s Blue Room Lounge, located south of Chicago, where he worked, according to a lawsuit filed by the attorney Gregory Kulis on behalf of Roberson’s family. Four other people sustained non life-threatening injuries in the shooting, including a man who was believed to have fired a gun before police arrived at the scene, Cook County sheriff’s spokesperson Sophia Ansari told the Associated Press.

Witnesses said Roberson, who was black, apprehended a man involved in the bar shooting after he opened fire. As police arrived, Roberson was holding “somebody on the ground with his knee in his back, with his gun in his back like, ‘Don’t move,'” witness Adam Harris told WGN9.

“Everyone was screaming out, ‘Security!’ He was a security guard,” Harris said. “And they still did their job, and saw a black man with a gun, and basically killed him.”

Midlothian Police Chief Daniel Delaney said officers from his department responded to the initial shooting and found multiple gunshot victims inside the bar, according to a statement from the Midlothian Police Department. Delaney said one Midlothian officer “encountered a subject with a gun and was involved in an officer-involved shooting.”

“The subject of the officer shot was later pronounced deceased at an area hospital,” Delaney said.

The Illinois State Police Public Integrity Task Force is investigating the officer-involved shooting, according to the statement.

The man who fired the initial shots at the bar, in what is believed to be a dispute, remains hospitalized, Ansari said. His name has not yet been publicly released. Charges are pending against him.

Ansari said Roberson, who was the father to a 9-month-old boy, was licensed to carry a firearm.

Kulis, an attorney representing Roberson’s family, has filed a civil rights lawsuit seeking more than $1 million. He said Roberson was wearing a hat that said “security” on it when he was shot.

Get The Brief. Sign up to receive the top stories you need to know right now. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Mahita Gajanan at mahita.gajanan@time.com.