The FBI-Chicago Field Office released images of the male suspect Wednesday in the hopes of identifying the wanted bank robber.
The suspect has worn disguises during recent crimes at banks in the Loop starting in mid-September, and then he changed clothes while on public transportation, the federal agency said.
The most recent bank robbery happened Tuesday, where the suspect handed a note to a teller demanding funds and made a violent threat before fleeing the scene, FBI officials said.
The suspect was described as man between the age of 30 to 40, with a height of about 5' 6" to 5' 7". He has been seen wearing a dark plaid patterned jacket, a white shirt with a collar, light-colored jeans, a black hat, mirrored sunglasses with a black frame, and black and white athletic shoes, the FBI said.
The "Bare-Chested Bandit" has an armband tattoo on his upper right arm, FBI officials said.
Anyone with information about the suspect can report a tip by calling 312-421-6700 or going to tips.fbi.gov.
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No further information about the bank robberies were immediately available.