A US Navy veteran has been taken into custody as a suspect in the investigation of letters sent to senior US government officials, initially feared to contain the poison ricin.
The letters were sent to Pentagon officials and President Donald Trump.
William Clyde Allen III was arrested at his home in Logan, Utah by the Federal Bureau of Investigation.
A spokeswoman for US attorney's office said that the 39-year-old will be charged tomorrow.
US officials say they have essentially ruled out terrorism in the case.
A Pentagon spokeswoman has said tests had revealed that the alert was triggered by castor seeds, which ricin is derived from, as opposed to the deadly substance itself.
Ricin is found naturally in castor seeds but it takes a deliberate act to convert it into a biological weapon.
Ricin can cause death within 36 to 72 hours of exposure to an amount as small as a pinhead - no known antidote exists.
