CHICAGO (CBS) — An off-duty Cook County Sheriff’s officer shot and killed one of three men who robbed him at gunpoint at a gas station in the Pullman neighborhood Monday night.

Shortly before 10 p.m., the off-duty sergeant was pumping gas at a Citgo near 103rd and Cottage Grove, when three men approached, and one of them pointed a gun at the officer.

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The robbers demanded the sergeant’s gun, and as he handed it over, one of the suspects rummaged through the officer’s car.

The officer then reached toward his back pocket, pulled his own gun, and shot the robber who had pointed the gun at him, killing the suspect.

CBS 2 has learned the robber who pulled the gun was 16-year-old Deonta Dewight.

CBS 2’s Suzanne Le Mignot talked to a man who says he knows Dewight. He agreed to speak with us if we concealed his identity.

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“It’s shocking to see somebody that you know, actually do something like that,” he said.

The two other suspects fled the scene with the sergeant’s wallet. Police have not caught them, as of early Monday.

Those pumping gas at this Pullman Citgo on 103rd near Cottage, were very outspoken about the shooting.

“They should be in bed at 10 o’clock at night. I would do the same thing. You know what I’m saying? It just needs to stop. We work hard for our money. To get anybody to take anything from us. That’s ridiculous,” said gas station customer Tamekia Kelly.

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The sheriff’s office said the sergeant was acting in self-defense. Chicago police were investigating.