MELISSA BLOCK, HOST:
And Tovia mentioned a different kind of attack, one that's the subject of a widening investigation here in Washington, D.C. A second letter thought to contain the poison ricin has been sent for further testing. That one was addressed to the White House. We heard yesterday about one addressed to Mississippi Senator Roger Wicker. Also today two Senate office buildings were locked down as the Capitol police investigated suspicious packages.
NPR's Tamara Keith joins us to talk about all this. And Tamara, first, we should say that the Senate office buildings are back to business as usual, but why don't you describe what happened earlier today?
TAMARA KEITH, BYLINE: It was pretty tense for a while there. There was announcement over loud speakers saying that people couldn't go on the first or the third floor of the Hart Senate office building that the third floor of the Russell office building was locked down. They were investigating - the Capitol police were investigating suspicious packages. The bomb squad was called in, though I think that was out of an abundance of caution.
And then, about an hour and a half later, everyone was given the all clear. A spokesperson for the Capitol police told me they were speaking to an individual, but that he was not detained. He was just talking to them. And I think the reason that this got so much attention is because of what happened in Boston and because of these ricin letters.
Because these suspicious package investigations actually happen here in the Capitol complex pretty frequently and obviously people are being more vigilant now because of Boston.
BLOCK: Well, let's turn to those letters. One, as we mentioned, was addressed to the White House, processed elsewhere, another one sent to Senator Wicker. There were reports of other suspicious letters as well today.
KEITH: Right. And the Secret Service says that it's looking into this letter that was addressed to the president. It was received yesterday in a remote White House mail screening facility and it contained a granular substance that, with a preliminary test, tested positive for the poison ricin and the letter to Senator Wicker was also intercepted at a remote facility and it also tested positive for ricin, which comes from castor beans.
But the FBI is quick to point out that these were preliminary positive tests and that that's not a definitive thing, that further testing is currently underway in a specialized lab and that takes 24 to 48 hours. They say this doesn't appear to be connected to the bombing in Boston and that there may be more letters to come.
BLOCK: And, in fact, there appear to be reports of other letters, one sent to Senator Carl Levin of Michigan, another to Arizona Senator Jeff Flake.
KEITH: And these were both in their district offices and in some way, they're not looking for suspicious letters and seeing suspicious letters, though Senator Flake recently tweeted that the suspicious package at his office had been cleared, no dangerous material and he thanked the United States Postal Service, the police department, FBI for their quick response. Everyone was safe, he said.
You know, since the anthrax letters, people have been on edge in the Capitol and even so many years later.
BLOCK: Okay. Tamara Keith on Capitol Hill. Tam, thanks.
KEITH: You're welcome. Transcript provided by NPR, Copyright NPR.