A man used a note to demand money from a teller at the Byline Bank located at 11157 S. Ewing Avenue in the East Side neighborhood just before 11 a.m., according to the FBI.
The suspect displayed a handgun and was seen wearing a black pea coat and surgical mask in a surveillance image released by the FBI.
The suspect got away with an unknown amount of money and remains at large.
Anyone with information is asked to report a tip to the FBI on tips.fbi.gov or by calling 312-421-6700. Tipsters can remain anonymous.
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