(CNN) - The FBI announced Thursday its agents are looking for a letter, this one directed to the Central Intelligence Agency, that it believes was similar to at least three other letters that contained ricin.
Letters were sent to a federal judge, a Spokane post office, President Barack Obama and Fairchild Air Force Base, the FBI said. Tests are being conducted on the letter sent to Fairchild Air Force Base to determine whether it - like those other three letter - contained ricin.