By Mike Brooks and Dana Bash, CNN
updated 6:30 PM EDT, Tue April 16, 2013
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.
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.
The envelope was addressed to a U.S. senator, though the sources would not say which one.