Surveillance pictures of the suspect were captured inside the store, located in the 13000 block of Lambert Road.
Investigators said the robber first held up the store at gunpoint on May 24th and then came back six days later. No injuries were reported in either incident.
The suspect is described as a Hispanic man, between 25 and 30 years old and about 5 feet 8 inches tall with a thin build.
He used a dark-colored handgun and has tattoos on both his face and arm.
Anyone with information on the suspect was urged to contact Whittier Police Detective Bolanos at (562) 567-9281 or the department's crime tip line at (562) 567-9299.