By Steven Graves

CHICAGO (CBS) — A man was shot and killed in a 24-hour Subway sandwich shop early Sunday in the East Side neighborhood.

Police late Sunday said the shooting was the result of a gang feud.

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Police said a 22-year-old man was inside the Subway at 106th Street and Avenue B – one street west of the Indiana state line – shortly after 2 a.m. A group of five or six men approached him and they got into a quarrel.

One of the men in the group pulled out a gun and shot the 22-year-old man in the head. He was left to die in the store.

The victim was identified as Frank Corona, according to the Cook County Medical Examiner’s office.

The suspects fled the scene in a black sport-utility vehicle.

As CBS 2’s Steven Graves reported, this was not the first time workers at that particular Southeast Side Subway have gone through terror.

Cleanup crews were seen scrubbing blood from the floor at the restaurant on Sunday afternoon. Regular customers were turned away.

They were met by a sign saying an “unfortunate incident” had closed the store.

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Hours before, police swarmed the store after the murder. Chicago Police Department spokesman Anthony Guglielmi tweeted Sunday afternoon that detectives have learned the shooting is linked to an escalating gang conflict several miles away on the West Side.

Everything was caught on camera.

A source who saw the video told CBS 2 a fist fight broke out between two groups. The shots were fired and Corona was killed as one group left the store, the source said.

One employee witnessed the whole thing. A woman who works nearby told CBS 2 she called a worker she knew.

“I’m like ‘OK, but everybody’s safe – the employees – and everything is good there?’ He’s like, ‘Everything is good,’” the woman said.

Her concern was heightened because of something that happened just weeks ago. A driver slammed into the restaurant and got away in October.

Police have no reason to think the two incidents are connected. But it does little to calm the nerves of those who come to the Subway every day.

“I don’t want to be here at all,” the woman said. “I’m scared.”

Police officers are familiar with Corona. His family asked for privacy.

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Area South detectives continued to comb through evidence Sunday night. Guglielmi said investigators were “combing through some very helpful digital evidence.”