Additionally, ABC News is reporting a second letter to a senator has been intercepted and is being tested.
The letter was received at the remote White House mail screening facility.There's no word yet which senator was the target of that second letter. Yesterday, a letter sent to Sen. Roger Wicker tested positive for ricin.
This facility routinely identifies letters or parcels that require secondary screening or scientific testing before delivery.
The Secret Service is working closely with the U.S. Capitol Police and the FBI in this investigation.
Meanwhile, law enforcement officials say a second letter sent to the U.S. Senate has been intercepted and is being tested for poisonous ricin.
Two officials told The Associated Press on Wednesday that the letter was being treated in the same manner as a separate one sent to Mississippi Sen. Roger Wicker and was undergoing field tests.
There's ongoing discussion in Brainwrap's diary.
9:09 AM PT: CNN is reporting that Capitol Police are investigating a suspicious package in Sen. Richard Shelby's office, and that they are questioning a man with a backpack in the area of the Hart office building.
The White House is going to hold a briefing on these issues any minute now.
9:18 AM PT: WH briefing begins. Carney says a letter addressed to the President was noticed to contain "suspicious" substance. The FBI has a lead on the letter. The FBI is also pursuing the Wicker letter. The President has been briefed on the letters.
9:23 AM PT: An update from CNN via email alert says that the FBI says the letter to the president has tested positive for ricin.9:58 AM PT: 10:00 AM PT: