Federal authorities have arrested a man in Logan, Utah, suspected of mailing threatening letters addressed to the Pentagon and the White House, some of which initially tested positive for the poison ricin. Subsequent tests determined the mailings contained a castor bean substance, an ingredient used to manufacture ricin, according to two federal officials.

William Clyde Allen III, a Navy veteran, was taken into custody in Utah on Wednesday, two days after the packages and letters were discovered at mailing facilities. The U.S. Attorney's Office in Salt Lake City said federal charges were expected to be filed Friday.

Allen served in the Navy for four years, leaving the service in 2002. The motive remains under investigation.

William Clyde Allen III Davis County, Utah, Jail

The FBI said Wednesday agents and law enforcement partners conducted an operation in Utah and potentially hazardous chemicals were involved. Individuals were asked to stay away from the area, but the Logan City Police Department said there was "no wider threat to public safety at this time."

None of the threatening mailings reached the Pentagon or White House.

Pentagon spokeswoman Dana White said Wednesday afternoon the substance addressed to Secretary of Defense James Mattis and Chief of Naval Operations John Richardson was castor seeds. According to the Centers for Disease Control and Prevention, if castor seeds are swallowed, ricin can be released and cause injury.

The letter addressed to Mattis, who is currently out of the country, also contained a 5-by-8 inch card with handwriting on it, but the content has not been made public. Ricin can cause death in 36 to 72 hours and can only be manufactured deliberately.

Pat Milton and Jeff Pegues contributed reporting.