Police on Monday released photographs of the suspect taken from video surveillance cameras at the Gascon station and food market at 443 Middle Country Rd.
At about 6 p.m. on Aug. 25, the suspect, wearing a gray, hooded adidas sweatshirt, showed a black handgun and demanded cash from the store's register, police said.
The clerk gave the gunman the cash and the gunman also took the clerk's cellphone before fleeing on foot, police said.
Anyone with information can call Crime Stoppers at 800-220-8477. All calls will be kept confidential.