The most recent robbery occurred on Oct. 6 at the East West Bank in the 500 block of Montgomery Street in San Francisco's Financial District.
Police said the suspect walked into the bank, brandished a handgun and demanded money from a teller, then ran away with an undisclosed amount of cash.
The man is also possibly responsible for three other bank robberies in San Francisco, a U.S. Bank on July 27, 2010, a City national Bank on June 21, 2010, and a Bank of the West on June 10, 2010, according to the FBI.
The suspect is described as a white man in his 50s who is between 5 feet 6 inches and 5 feet 8 inches tall, between 150 and 160 pounds, has a slim build, short white hair and wears tinted eyeglasses, officials said.
He walked with a cane in one of the robberies and is known to wear plaid shirts.
Anyone with information about the identity or whereabouts of the suspect is urged to contact the FBI's San Francisco office at (415) 553-7400.
