An Iranian national arrested at the Mexican border has confessed to dozens of bank robberies in Southern California attributed to the so-called "FedEx Bandit," the FBI said Tuesday.

Farzad Naroii, 40, was detained by U.S. authorities while trying to enter the United States on foot at San Diego's San Ysidro border (search) crossing Monday afternoon, said FBI spokeswoman April Langwell.

Naroii, who lived in Tijuana, Mexico, admitted to 43 robberies during five hours of questioning, she said. He was in San Diego County (search) jail Tuesday on $1 million bail, pending formal charges.

Since 2003, Naroii allegedly stole about $300,000 in San Diego County, and other amounts in Los Angeles and Orange counties. The robber in the heists demanded that bank tellers deposit cash in FedEx (search) envelopes.

Investigators got their big break in June when Naroii, who was in the U.S. illegally, left his cell phone behind in a heist of a bank in Del Mar, north of San Diego, Langwell said. They used phone numbers to track his movements.