Police closed several roads around the Pentagon in Virginia yesterday after arresting a man whom they found with suspicious materials in his backpack.
A spokesman said they found the man in nearby Arlington National Cemetery before dawn and traced him to a car abandoned near the Pentagon.
His pack contained a compound initially believed to be ammonium nitrate, which can be used to make bombs. An FBI agent confirmed the substance was not explosive but would need further investigation. No device was found in the pack.