Frank Harrill, the supervisory senior resident agent of the FBI in Spokane, said in an email that workers at a post office in the city discovered the letter Saturday after it was returned as undeliverable. It had been addressed to the Central Intelligence Agency.
Harrill said the letter is similar in appearance to four other letters sent from Spokane last month that contained the deadly poison. Those were addressed to President Barack Obama, a federal judge, a Spokane post office and the nearby Fairchild Air Force Base.
No one has been sickened. The newly discovered letter was being sent for further testing.
A Spokane man named Matthew Ryan Buquet faces a one-count grand jury indictment for mailing threatening communications in connection with the case.