The branch in La Mesa was robbed twice on Monday - by two different robbers.
The men the FBI call "The Hard Hat Bandit" and "The Chatty Bandit" each robbed the branch about three hours apart, authorities said.
FBI spokeswoman April Langwell says "The Chatty Bandit" walked in to the branch about 3 p.m., showed a pistol and demanded cash.
Less than three hours later "The Hard Hat Bandit" walked in and presented a note demanding money.
The FBI believes "The Chatty Bandit" has held up nine banks since March and "The Hard Hat Bandit" has struck three times this week. Neither has been arrested.