Patrol officers were called to the Subway on the 3900 block of Broadway in southeast Houston around 8pm, where they found a male employee in his late teens who had suffered a gunshot wound to the neck.
The employee was taken to a local hospital for medical treatment, where he later died.
Police say the two suspects walked into the restaurant and pointed the gun at the victim's mother. He then took the bullet in his neck to protect her.
They were both Subway employees. No customers were in the restaurant at the time of the shooting.
Investigators are looking for two males who fled in a "tan, foreign, small car." Another robbery occurred at a nearby Subway restaurant, and police are looking into whether the two may be related.
No other details have been released.