The man died, and Thursday night, police were hoping images of a white SUV would help lead to an arrest.
Witnesses say two teenagers inside the store were the intended targets.
The shooting happened on the Southeast Side Thursday morning in the 2700-block of E. 79th St.
Police said Thursday night they had no one in custody, but they may have several strong leads, including that white SUV.
They are also looking to talk with two suspected gang members who may have been the intended target of the gunman.
Investigators were on the scene Thursday night looking for evidence to help them find the gunman who fired a single shot through the glass at Margarita's Meat Market. The bullet was apparently intended for two teenagers who witnesses say had been exchanging gang signs with teens in a white SUV.
The SUV drove by several times. The last time, a passenger fired the shot that hit store employee Alfredo Cuellar Chavez, 41, in the chest, killing him.
"Alfredo was a real good guy. He was the only one out here from his family from Mexico. He worked, sent money - half his check went over there - more than half. That's all he worked for, was for his family," Gilbert Figeroa said.
Minutes before the shooting, Cuellar Chavez can be seen in the video working behind the counter. The father of four children, he had worked at the store for several years and was well-liked in the neighborhood. Friends left mementos in front of the store Thursday.
"Never make trouble, no drink or smoke or nothing, only come and work," storeowner Fernando Chavez said of Cuellar Chavez.
Security cameras show an employee next door hitting the floor as the shot rang out. Police are hopeful that a blue light camera stationed just outside the market may have captured the license plate of the white SUV.
Employees say the teens who were the apparent target have been in the store often and were considered trouble makers who were usually asked to leave. They were still inside the market on their phones when a female employee ran in and called 911 after finding Cuellar Chavez on the ground.
"They ran off like nothing," said Figeroa. "The bullet missed them - that's what happened."
Relatives say most of Cuellar Chavez's family is in Mexico, including several of his children and his fiancee. They are working on funeral arrangements, and they say the services will likely take place in his hometown of Juarez, Mexico.