The FBI is asking for help catching two wily thieves it has dubbed the "backpack bomber bandits," believed to have orchestrated eight robberies of seven banks in the Los Angeles area.

The men, one white and one black, carry a backpack they claim contains a bomb when they go into banks and demand money, the FBI said. While only one man commits each robbery, the FBI suspects the pair is acting in concert.

The latest strike happened Wednesday, when the black suspect robbed a Bank of the West in Santa Ana, Calif.

The bandits usually wear baseball caps or hats, carry almost identical gear — either a backpack or black gym bag — and make similar threats about carrying a bomb. They hand bank tellers written notes demanding undisclosed amounts of cash, said Laura Eimiller, a spokeswoman for the FBI's Los Angeles bureau.

"We believe that somebody knows who they are, possibly," Eimiller told FOXNews.com. "They could be transients trying to feed a drug or gambling habit, but they have not yet been identified."

No one has been physically hurt in the robberies, she said. A witness saw a black man and a white man leaving one of the crime scenes in a car together.

The robbers, acting separately, are believed to have held up a Union Bank in Santa Monica, Calif., and Washington Mutual branches in Hawthorne, Anaheim, Westminster, Santa Monica and Fountain Valley, the FBI said. Both robbed the same bank, the Hawthorne Washington Mutual, within a very short period of time.

With their latest suspected hit at the Santa Ana Bank of the West, they are wanted in eight separate incidents, all in Los Angeles and Orange counties.

Tips have been pouring in and the FBI has some leads, Eimiller said, adding that the FBI is confident the robbers will be caught.

The white male has been seen with a handgun in his waistband, according to authorities. He is described as being 6-foot, 170 pounds and in his late 40s. He wears prescription eyeglasses and a silver wedding band.

The black male is said to be 6-foot-3, between 180 and 200 pounds and in his early 40s with a mustache.

The FBI has released surveillance photos and is appealing to the public for help, asking anyone with information to call 310-477-6565. An undisclosed reward is available.