Ricin is a poison that is naturally found in castor beans, produced by the pervasive castor bean weed. It can be formed into a powder, mist or pellet, or even added to water, according to the federal Centers for Disease Control and Prevention. Because

(LIN) — On Wednesday, the Secret Service investigated a "suspicious" letter delivered to President Barack Obama. An investigation revealed that the letter contained a poisonous substance called ricin. This comes one day after a letter mailed to Sen.

(LIN) — On Wednesday, the Secret Service investigated a "suspicious" letter delivered to President Barack Obama. An investigation revealed that the letter contained a poisonous substance called ricin. This comes one day after a letter mailed to Sen.

The ghastly bombings in Boston followed by envelopes laced with the lethal poison ricin that were sent to the U.S Capitol and the White House, renew fears about our vulnerability to these kinds of terrorist acts. It invites unwelcome memories of 9-11.

It was not immediately clear when the envelope was received. But it arrived in a Senate mail facility, which has now been closed for more testing. All congressional mail will now be processed through the U.S. House facility.

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