From the Chicago Tribune (November 1, 2015):
The dead man has been identified as Reginald Gildersleeve, 55, of the 5000 block of South California Avenue, according to the Cook County medical examiner’s office. Gildersleeve was pronounced dead on the scene at 7:10 p.m. . . .
Citing preliminary information, police said a man walked into a store around 7 p.m. in the 2700 block of West 51st Street in the Gage Park neighborhood on the Southwest Side, announced a robbery to an employee working behind the counter and displayed a handgun.
Another employee came from the back of the store and the gunman pointed his weapon at her, police said. He then made her go to the back of the store, which also serves as a currency exchange.
After that, a customer who was also inside the business pulled out a gun and opened fire at the robber, killing him, police said. . . .
From the Chicago Sun-Times:
[Chicago Police Department spokesman Anthony Guglielmi] said Gildersleeve had an extensive criminal history, including prior arrests for robbery. . . .