It happened just after 11 p.m. Monday at Rose Family Grocery Store in East New York.
Police say 25-year-old Edwin Candelario attempted to attack the worker with a knife during an argument.
That's when the 34-year-old worker pulled out a gun and police say he shot Candelario several times, killing him.
It appears the worker was not licensed to have the gun.
A knife was found at the scene.
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