Letters containing a white powder were sent to the district offices of at least four Alabama Members of Congress on Monday, sparking an anthrax scare and an FBI investigation.By Monday afternoon, all the offices appeared to be cleared. Special Agent Angela Tobon, an FBI spokeswoman in Mobile, Ala., said nine “threatening letters— were sent to lawmakers, ostensibly from the same source. GOP Sen. Richard Shelby’s office received the latest one at about 4:30 p.m. Monday, but so far, tests have shown that the substance isn’t hazardous.The letters were sent to the district offices of Shelby, GOP Sen. Jeff Sessions and GOP Reps. Jo Bonner and Mike Rogers, Tobon said. Capitol Police spokeswoman Sgt. Kimberly Schneider said the department is working with the FBI on the case but declined to discuss any details.Earlier on Monday, Bonner and his district staffers spent hours quarantined in their Mobile offices, according to Bonner spokesman Mike Lewis. Bonner staffers had opened the letters — one each sent to the Mobile and Foley offices — on Monday morning.“These letters were set aside, and we notified law enforcement,— Lewis said. “Our understanding is that each of these letters contained some powder in a sealed plastic bag.—The offices have since been cleared, and the Mobile office is now open, Lewis said. The office in Foley will probably open Tuesday morning, he said.At least one of Rogers’ offices opened earlier Monday. Spokeswoman Shea Snider said two of his three district offices each received a suspicious letter. The Anniston office was “only shut down for a few hours because the powder was tested and cleared quickly,— she said, while the Montgomery office remained closed at 4 p.m. Monday.Shelby spokesman Jonathan Graffeo referred questions to the FBI, while a spokeswoman for Sessions did not immediately return a request for comment.