An employee shot and killed a robber inside a Metro PCS store in Southwest Philadelphia, according to investigators.

Police said an unidentified man in his late 30s armed with a gun tried to rob the store on 70th Street and Elmwood Avenue shortly after 4 p.m. Monday.

NBC10 obtained surveillance video from inside the store showing the suspect walking inside, displaying a weapon and throwing a bag on the counter in front of the employee. The employee, who investigators said has a permit to carry, then quickly pulled out his own gun and opened fire, shooting the suspect multiple times.

"Out of nowhere I heard like ten shots go off," a witness, who did not want to be identified, told NBC10.

The suspect was pronounced dead at the scene at 4:12 p.m. by medics.

On Tuesday, a spokesperson told NBC10 the homicide unit for the Philadelphia District Attorney's Office determined the shooting was justified.

"After reviewing video of the incident the DAO homicide unit has concurred with the Philadelphia Police Department that this was a justified self-defense shooting consistent with Pennsylvania law," the spokesperson wrote.

The employee, who sources say is a Marine reservist, was not hurt during the incident and was the only other person inside the store.

"He ran to the store next door," a witness said. "He looked scared and like he was panicking."

Police told NBC10 the store had been robbed twice within the past year prior to Monday's incident.