According to a spokesperson for the St. Louis Metropolitan Police Department, the teen walked in the Galaxy Balloon Shop at around noon pretending to be a customer.
The teen walked up to the counter with merchandise but instead of pulling out his wallet, the store owner said the teen opened his jacket, displayed a gun, and asked for money from the register.
The store owner pulled out a gun from behind the counter and shot the suspect.
Investigators said the teen's weapon turned out to be a toy or replica gun.
"Well, right now we are not looking for any other suspects. The suspect was taken to the hospital and we are questioning the shop owner and verifying everything he had to tell us," said Captain Mary Warnecke, Commander Investigative Services for the SLMPD.