Police said the shooting happened in the South Shore neighborhood's 2300-block of East 79th Street just after 7:15 p.m.
Three offenders wearing face coverings entered the store, police said. One of them took out a gun and pistol-whipped an unarmed security guard in the face.
Police said the group was running away when someone outside of the store took out a gun and shot one of them, a 60-year-old man, in the chest.
The 60-year-old suspect was taken to the University of Chicago Medical Center in critical condition. Officers recovered a gun from the man, and he is in police custody at the hospital.
That shooter, along with the other two suspects, got away.
Charges are pending, and detectives are still looking for the other three people involved.
Area Two detectives are investigating.
Police did not immediately provide further information.
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