It happened at a 7-Eleven on Little East Neck Road in West Babylon on Wednesday around 9 p.m.
Surveillance video shows the masked suspect pointing a gun at the clerk. He demanded cash, which the worker handed over immediately.
Suffolk County police's detectives continue to investigate.
Detectives are asking anyone with information on the robbery to call the First Squad at 631-854-8152 or call anonymously to Crime Stoppers at 1-800-220-TIPS.
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