WARNING GRAPHIC CONTENT: An off-duty Cook County Sheriff's sergeant shot and killed a man who tried to rob him Monday night at a Far South Side gas station. (Posted on: February 11, 2014)

A gun pointed at his gut, the off-duty sheriff's sergeant digs through his pockets with his left hand, fumbling for money, as the three robbers surround him at the Far South Side gas station.

The sergeant is surer with his right hand, quickly drawing his own gun and firing point-blank. The gunman, 16, drops at his feet as the two others scatter, according to surveillance video that captured the robbery Monday night at a Citgo station at 103rd Street and Cottage Grove Avenue, across the street from Gately Stadium.

The sergeant swings around at the fleeing robbers, then points the gun down as the gunman struggles to get up. The video shows the sergeant kicking away the robber's gun and then opening the passenger door of his own car, apparently to get his phone.

The 16-year-old, Deonta Dewight Mackey, was shot in the head and died at the scene, according to police. He lived in the 900 block of East 104th Street, about four blocks from where he died.

The sergeant was not injured, and police said they were still looking for the two other robbers.

The shooting occurred around 10 p.m. as the sergeant was filling his car at the Citgo station, police said.

The surveillance video shows a man, a gun in his right hand, running up to the sergeant and pointing the gun at him. The sergeant backs way, drops the nozzle and raises his hands, according to the video. Two other men run up and join the gunman, according to the video.

The sergeant appears to hand something over to the gunman, then continues digging through his pockets with his left hand, the video shows. Then the sergeant's right hand quickly swings around and the sergeant fires at the gunman, according to the video.

Earlier Monday, another man was shot in his ankle about 7:25 p.m. on the 5800 block of South Princeton Avenue in the Englewood neighborhood, Alfaro said.

The man was taken to Saint Bernard Hospital and Health Care Center, he said.

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