That man was one of at least two suspects who entered Ms. Jessie's Stop and Shop in the 900 block of South 12th Street around 8:40 a.m.
The man killed suffered a gunshot wound to the head, police say. He has not been identified.
Another suspect, a 22-year-old man, was arrested a short time later.
Two weapons were recovered at the scene, police say. However, it remains unclear whose gun - the suspect's or the store owner's - was used in the deadly incident.
The store owner was not injured and is currently being questioned by investigators.
People in the community described a store owner as a "good guy," adding that he worked at the store with his wife.
Neighbor Louise Hanible spoke highly of the store owner, telling us, "Everybody in the neighborhood loved him. And his wife and all them was born and raised in this neighborhood. Been in this neighborhood all they life... They (the suspects) came in the wrong neighborhood."
Police say there is the possibility of a third suspect, who got away.
Nearby schools were briefly placed on lockdown, but the lockdown has since been lifted.