Fairfax County saw more than double the number of bank robberies this year compared to 2005 and the highest count in nine years — a phenomenon that remains unexplained.

As of Tuesday, 43 banks had been robbed in the county in 2006, 32 of which police have closed with arrests, according to information provided by the Fairfax County Police Department. Last year, there were 19 bank robberies, and 18 the year before that.