An employee of a JJ Fish & Chicken restaurant allegedly shot and killed two customers during an argument Monday night on the Southwest Side. Two unidentified men, 55 and 56, were quarreling with the male employee inside the restaurant, 7828 S. Western Ave., when the employee opened fire around 10:30 p.m., Chicago police said. The younger man was shot in the face and the older man was shot in the head, police said. Both were dead at the scene.The Cook County medical examiner's office confirmed the deaths but had not released their identities late Tuesday morning.The restaurant remained closed late Tuesday morning in a strip mall near Western Avenue and 79th Street, though its open sign remained flashing. There were no apparent signs that a double slaying had happened there the night before.A woman who showed up to buy chicken for her workplace was disappointed to learn the restaurant was closed and was sad to hear about the double murder."I wish they didn't have done that," said the woman, who asked not to be named.Most of the other businesses in the mall were vacant: a former Chinese food restaurant, a clothing store and cellphone store. Employees of a car insurance business said they were closed at the time of the shooting and were unaware of the details.Area One detectives are investigating, and no arrests were made, police said.