Illinois state police on Tuesday were investigating a white officer over the fatal shooting of a black security guard who had apprehended a suspected gunman at a bar outside Chicago, officials said.
The officer was placed on administrative leave after the incident, which took place in the early hours of Sunday at Manny's Blue Room Lounge in the town of Robbins, 32 kilometres south of the Midwestern city.
The security guard, 26-year-old Jemel Roberson, was working at the bar, and intervened when an argument erupted and someone started shooting.
Several local police forces responded to the incident, in which several people were wounded.
A police officer from the nearby village of Midlothian arrived at the scene and shot Roberson, despite the guard wearing a uniform with "security" emblazoned on it, according to witnesses.
"(Roberson) had somebody on the ground with his knee in back, with his gun in his back, like, 'Don't move,'" witness Adam Harris told Chicago television station WGN.
"Everybody was screaming out, 'Security!' He was a security guard," Harris said, but police "saw a black man with a gun, and basically killed him."
Roberson died of his injuries at hospital.
The officer under investigation has not been formally identified, but a clerk at the department confirmed the officer was white, and was placed on administrative leave pending the inquiry.
Roberson's family has sued the village of Midlothian and the unnamed officer over his death, alleging that the shooting was "excessive and unreasonable."
Midlothian Police Chief Daniel Delaney, who supervises a force of 34 officers, said the state police was investigating the shooting in order to "ensure transparency and maintain public trust."
The Illinois State Police has not formally commented on the incident.
Roberson reportedly was an aspiring police officer.
An online GoFundMe campaign had raised more than $78,000 to pay for Roberson's funeral expenses.
The shooting was the latest in a long line of deadly encounters between police and African Americans - highly-publicized on social media and often caught on video - that sparked the Black Lives Matter movement.
