there is a story, still fragmentary, about an envelope sent to the office of Sen.Roger Wicker (R - MS) that was intercepted in a mail processing facility when it tested positive for Ricin, a deadly poison made from castor beans. CNN, which reported the story a short while ago, did NOT name the Senator. An Email from Politico attributes the naming to the AP.
According to the CNN report, the envelope was tested two more times, and each time came up positive for ricin.
Fran Fragos Townsend, who serves as a consultant to CNN, noted that some Al Qaeda material discusses ricin. However, the first apparent use as a weapon was to assassinate Georgi Markov, a Bulgarian dissident killed in London, apparently by Soviet agents.
So far there is no evidence that the envelope is in any way related to the bombing of the Marathon in Boston.
NOTE - I have added some additional material in the comment thread below. Another diary on the subject went up while I was writing this, and it will probably draw the majority of the attention. It is immediately below this in recent diaries.
additional note - it is worth scanning the Wikipedia article on ricin, where you will learn that the US explored weaponizing ricin, including plans to manufacture during WWII, but then abandoned that, and that even post-war exploration was dropped and replaced by the manufacture of sarin, which was the gas used by the Japanese cult in its attack. It is relatively easy to manufacture, and it does occur naturally.
Sen. Wicker now has a protective detail, according to CNN.
Last note - Joan McCarter has now posted on the front page about this, with links to both diaries, mine and AlyoshaKaramazov's.
UPDATE AT &:!!:CNN now reporting first test posting, second negative, third inconclusive, which is why it is being sent to another lab for a more detailed test. The field tests in the processing facility are apparently not all that reliable.