Officials said around 4:20 a.m., police were called to the Firing Line Gun Range and Gun Store.
Officers said when they arrived at the store they found a man on the second floor with a gunshot wound to the head. He was pronounced dead at the scene.
Investigators said the gun shop owner told them he was staking out his store following an earlier burglary attempt. He said he watched the security screen show three or four men use wire cutters to break through the gate and enter the store.
The owner said he pointed his gun at the man inside the store and fired, striking him in the head. The two to three other people ran from the scene.
Officials said another person arrived at Thomas Jefferson University Hospital with a gunshot wound to his shoulder. Police are unsure if this shooting is connected to the incident at this time.
Police said the owner of the gun store is cooperating with the investigation.