Police mistakenly shoot dead a security guard who was trying to stop a gunman

Security guard Jemel Roberson. Photo / CBS

A black security guard has been fatally shot by police after he stopped a customer who had opened fire at a bar in Illinois.

Witnesses say the armed guard was trying to detain an armed man following a shooting at a suburban Chicago bar, authorities said.

Investigators said 26-year-old Jemel Roberson was pronounced dead shortly after being taken to a hospital following the shooting at Manny's Blue Room in Robbins, just south of Chicago.

Four other people were shot and wounded during the incident, including a man who police believe fired a gun before police arrived, Cook County sheriff's spokeswoman Sophia Ansari said.

When police arrived at the scene, Roberson was holding "somebody on the ground with his knee in his back, with his gun in his back," witness Adam Harris told WGN-TV.

"Everybody is screaming out, 'He's a security guard,"' Harris said.

Roberson was licensed to carry a firearm, Ansari said.

Charges were pending against the man who investigators believe fired the initial shots during a dispute. His name has yet to be released, and he remained hospitalised, Anasari said.

Investigators said the initial gunfire was reported around 4 am.

An officer responding from nearby Midlothian encountered and shot "a subject with a gun," Midlothian Police Chief Daniel Delaney said in a statement. The person was later identified as Roberson.

No details have been released about the officer.

Roberson was the only person killed in the shooting. The other four people who were shot suffered wounds that weren't considered life-threatening, Anasari said.

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

The Rev Marvin Hunter said Roberson was a promising keyboard player who played at his and several other area churches.

"He was an upstanding young man who was trying to get custody of his son and get enough money together for a deposit on a new apartment," said Hunter, the great uncle of Laquan McDonald, a black teenager fatally shot in 2014 by a white Chicago police officer

Patricia Hill, the pastor of Purposed Hill in Chicago, said that Roberson had dreamed of being a police officer.

Hill told WGN-TV: "The very people that he wanted to be family with took his life."

- AP