FBI agents have arrested a man after a pair of letters containing the deadly poison ricin were discovered in Washington state last week.
Matthew Ryan Buquet, 37, was expected to make his initial appearance in federal court in Spokane.
The letters were postmarked in Spokane and addressed to the downtown post office and the adjacent federal building. They were intercepted by the Postal Service, and no one was injured.
Investigators in hazardous materials suits spent most of Saturday executing a search warrant at a three-story apartment building downtown but said there was no public health risk. Witnesses reported that agents escorted a man from the building.
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.
There have been no reports of illness connected to the letters. The Postal Service has said the ricin was in a crude form that did not pose a health risk to its employees.
The Spokane investigation comes a month after letters containing ricin were addressed to President Barack Obama, a US senator and a Mississippi judge. A Mississippi man was arrested in that case.