The shooting happened around 8 p.m. in the 400 block of Merrill Avenue in Calumet City, police said.
The victim, a 23-year-old man, was shot in the upper body after he was robbed during a food delivery, Calumet City police said. Officers provided trauma care to the victim.
The man was taken to a hospital, and he was later pronounced dead.
The Cook County Medical Examiner later said the homicide victim has been identified as 23-year-old Steven Cotner, who was shot in the back.
The victim's sister, Allison Cotner, told ABC7 she was the one delivering the pizza, and her brother was with her, working as security, when two armed robbers approached her car.
"A guy wearing all black and a ski mask came on my side and pointed a gun and said give me the money," Allison said.
Allison said she had no money. She was delivering for Windy City pizza, and Steven was also in training to become a pizza delivery driver himself. The manager told ABC7 that drivers carry no cash.
"So then, my brother started tussling with the guy and trying to protect me..." Allison said.
She said one of the suspects ran and moments later she heard two gunshots, and her brother was later pronounced dead. The left side of Allison's face was bruised after the altercation, and she has stitches near her eye, but she survived.
There was no information available about any possible suspects, no arrests have been made.
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Calumet city police investigators went door to door through the neighborhood Friday afternoon, looking for witnesses and any possible evidence. They said it does not appear the victims were targeted, more likely it was a robbery gone bad.
That's a little consolation to family members who are grieving.
"I lost my only son, and I can't get him back for anything," the victim's mother, Martina Lohrbach, said.
Family members said they're praying the suspects will turn themselves in. They want justice.
"They didn't even get nothing," Allison said. "They took my brother for no reason."
The Calumet City Police Department and the South Suburban Major Crimes Task Force continue to investigate.
No further information was immediately available.