Updated: 3:33 p.m.Letters containing a white powder were sent to the district offices of four Alabama Members of Congress on Monday morning, sparking an anthrax scare and an FBI investigation.Special Agent Angela Tobon, an FBI spokeswoman in Mobile, Ala., said Monday afternoon that tests had so far shown the substance isn’t hazardous. The agency hasn’t yet tested all the letters, she said, but officials hope to be done by the end of the day. The “threatening letters— were sent to the district offices of GOP Reps. Jo Bonner and Mike Rogers and GOP Sens. Richard Shelby and Jeff Sessions, 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.Bonner and his district staffers remained quarantined in their Mobile offices Monday afternoon, according to Bonner spokesman Mike Lewis. 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.—Staffers in the Mobile office remain inside, Lewis said, but he was not able to confirm whether staffers in Foley were similarly quarantined. The offices will remain closed while the FBI analyzes the letters, but Lewis said staffers did not open the plastic bag that contained the powdery substance. Two of Rogers’ three district offices each received a letter with the white powder, spokeswoman Shea Snider said. The Anniston office has reopened, she said, while the Montgomery office is closed pending the FBI’s testing of the substance.Lewis said he did not know what was written in the letters.He said he had not spoken to Bonner in “a while,— but he added, “We have heard from him this morning.—“We’re just waiting,— he said. “We hope it will be [cleared] soon.—Spokesmen for Shelby and Sessions did not immediately respond to calls about the incident.