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SPOKANE, Wash. -- Two letters that contained the deadly poison ricin have been intercepted at a U.S. Postal Service facility in Spokane this week.

The FBI says there have been no reports of illness connected to the letters, which were intercepted Tuesday.

The FBI, along with Postal Service investigators, are searching for the sender of the letters, which were postmarked Tuesday in Spokane.

Ricin is a highly toxic substance made from castor beans.

As little as 500 micrograms, the size of the head of a pin, can kill an adult if inhaled or ingested.

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