The owner of a gun store in South Philadelphia shot and killed a potential looter who broke in early Tuesday morning.Like many gun store owners these days, Gregory Isabella spent the night in his South Philly shop on guard after previous break-in attempts.He was ready when, about 4:15 a.m. Tuesday, a group of four men cut the lock and kicked in the door at Firing Line Inc. on the 1500 block of South Front Street. Isabella, 67, told police he was on the second floor when he heard them approach. He then shot and killed one of the alleged looters.By day, hundreds of residents wait in long...…The owner of a gun store in South Philadelphia shot and killed a potential looter who broke in early Tuesday morning.Like many gun store owners these days, Gregory Isabella spent the night in his South Philly shop on guard after previous break-in attempts.He was ready when, about 4:15 a.m. Tuesday, a group of four men cut the lock and kicked in the door at Firing Line Inc. on the 1500 block of South Front Street. Isabella, 67, told police he was on the second floor when he heard them approach. He then shot and killed one of the alleged looters.By day, hundreds of residents wait in long...WW…