Workers finished fumigating the Hart Senate Office Building and should know within a week whether they successfully removed deadly anthrax spores delivered in a tainted letter in mid-October.
Environmental Protection Agency spokeswoman Jennifer Browne said contractors finished releasing chlorine dioxide gas into the building's ventilation system around 2:30 a.m.
Afterward, crews collected "spore strips" covered with harmless test bacteria that should "tell us how effective we were in the fumigation process," Browne said.
The anthrax attacks hit the nation's capital Oct. 15 with the delivery of a letter to the Hart offices of Senate Majority Leader Tom Daschle (D-S.D.). Two days later, the building was closed, displacing 50 senators, their aides and other employees who work in the building.