Ronald Hosko, special agent in charge with the FBI's Washington field office, said there have been a dozen armored car robberies in the city since March 2010. He said that's in contrast to the roughly two to four such robberies or attempts in the city in the past several years.
Hosko told The Associated Press Thursday that the robbery increase "has our attention," and that officials are exploring links between the cases.
No one has been killed in any of the robberies, and Hosko won't say how much money has been stolen.
Arrests have been made in four of the 12 cases.