Suhrid Das, 48, who was popular in the neighbourhood, was shot on Wednesday night after being confronted by the assailant when he was closing down his store.
A break-in and robbery at another house in the same building just eight hours later led to suspicions that a robbery might be a cause of the killing, WSB Atlanta TV reported.
Banna Grocery was one of four businesses in the two-storey brick building in the Atlanta neighbourhood, and the people residing in the building described Das as a good-natured man.
When police officials rushed to the site responding to a call, they found the storeowner down from a gunshot wound to the abdomen, Atlanta police spokeswoman Kim Jones was quoted as saying by other media reports. Das was taken to a hospital but he later succumbed to his injury.
"Witnesses stated that the victim was closing up the store when he was confronted by an unknown assailant and shot one time," Jones said. Investigators said Das was shot in an apparent robbery attempt.
Taria Camerino, a co-owner of a candy store at the same building said a robber also targeted her store. She described Das a "very nice" man. "We would chat sometimes... He always seemed really sweet," Camerino said.
The police are investigating whether the same person was behind the shooting and the robbery at her store. Others said the building was "a little on edge" after the shooting incident.
"I'd hate to see him (Das) go out like that because he's a good man," Jimbo Billups, another resident, said. The neighbours said Das had been robbed two or three times in the past as well. "They didn't have to hurt him," said Billups.
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