(CNN) A Utah man has admitted to sending letters that tested positive for ricin to President Donald Trump and top government officials, according to a probable cause statement obtained by CNN affiliate KTVX.

According to the affidavit, in an interview after being taken into custody, William Clyde Allen III confessed Wednesday to having sent four letters with ground castor beans to Trump, FBI Director Chris Wray, Secretary of Defense James Mattis, and chief of naval operations Adm. John Richardson.

All four letters tested positive for ricin, a highly toxic compound extracted from castor beans, according to the affidavit. Allen was arrested on terrorist threat charges Wednesday afternoon, the document says.

Allen previously served in the US Navy as an enlisted sailor from 1998 to 2002.

On Monday, two of the suspicious pieces of mail were delivered to the Pentagon mail facility and initially tested positive for ricin, according to a US defense official.

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