A gunman held up the cashier at the Quick Pick Convenience Store on Tremont Street in Roxbury Sunday morning, the second armed robbery at the store this month. Boston police said that around 9:30 a.m., the suspect — whom they described as a light-skinned Hispanic man wearing a dark hooded sweatshirt, baseball cap, and dark face mask — went behind the counter, brandished a large silver weapon, and told the cashier, “If you move I’m going to kill you.” Police did not say how much cash was taken. Boston police spokeswoman Neva Coakley said the store was also robbed at gunpoint around 8:30 a.m. on Nov. 12. The suspect in that robbery was described as a white man, possibly Hispanic, wearing a gray hooded sweatshirt, white pants, and a checkered scarf over his face. He made away with an undetermined amount of cash, and has yet to be caught, Coakley said. The robberies are under investigation, and police have not determined if the suspect in each robbery is the same person, she said.