The family of Jemel Roberson, the “hero” security guard who apprehended a gunman in a bar before being shot and killed by a police officer, has filed a $1m lawsuit.

Roberson apprehended the gunman who had fired shots in the back, before tackling him and holding him until the police arrive on the scene by kneeling on his back. When the cops finally arrived, they mistook Roberson for one of the gunmen an shot him dead.

It is being reported that Roberson was holding his own licensed gun and wearing a hat emblazoned with “Security” when the officer opened fire. Four other people were shot and wounded.

“He had somebody on the ground with his knee in back, with his gun in his back like, ‘Don’t move,’” Adam Harris, a witness, told WGN 9. “Everybody was screaming out, ‘He was a security guard,’” Mr Harris said. “And they basically saw a black man with a gun and killed him”.

Attorney Gregory Kulis filed the civil rights lawsuit for the Roberson family who is seeking more than $1m on behalf of Roberson’s mother, Beatrice Roberson.

“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,” Daniel Delaney, the chief of the Midlothian Police Department, said in a statement posted on the department’s Facebook page.

Illinois State Police are handling the investigation into Roberson’s shooting.