Washington (CNN) -- An envelope that tested positive for the deadly poison ricin was intercepted Tuesday afternoon at the U.S. Capitol's off-site mail facility in Washington, congressional and law enforcement sources tell CNN.
Senate Majority Leader Harry Reid said he was told the letter was addressed to the office of Sen. Roger Wicker, R-Mississippi. After the envelope tested positive in a first routine test, it was retested two more times, each time coming up positive, the law enforcement source said. The package was then sent to a Maryland lab for further testing.
Senators were briefed on the matter Tuesday evening and told the congressional post offices would be temporarily shut down.
"It was caught in the screening facility. That's why we have an off-site screening facility for mail," said Sen. Claire McCaskill, D-Missouri.