Federal prosecutors have filed additional charges against a Navy veteran in Utah accused of sending letters containing the substance from which ricin is derived to key members of the Trump administration, according to an indictment unsealed Thursday.

William Clyde Allen III, 39, was arrested earlier this month after authorities intercepted envelopes containing ground castor beans that were addressed to President Trump, Defense Secretary Jim Mattis, Chief of Naval Operations Adm. John Richardson, and FBI Director Chris Wray. According to the indictment, authorities also intercepted envelopes that were addressed to CIA Director Gina Haspel and Air Force Secretary Dr. Heather Wilson.

Allen has pleaded not guilty to seven charges, including threatening to use a biological toxin as a weapon, mailing a threat against the president and mailing threatening communications to an officer of the United States. He allegedly told investigators he bought hundreds of castor beans on eBay to "defend our nation" if "World War III broke out."

All six envelopes were mailed on the same day and bore Allen's return address, prosecutors said, adding that the accompanying letters bore the phrase, "Jack and the Missile Bean Stock Powder."

No one was hurt in connection with the letters, which all tested positive for ricin.

Allen served in the Navy from 1998 to 2002. He has a criminal record in Utah including child abuse and attempted aggravated assault.

He's also had a history of sending threatening emails to then-President Barack Obama, the Air Force and the state of Utah, investigators said.

A judge decided Monday to keep Allen in jail ahead of trial, despite a request that he's needed at home to care for his wife, who suffers from a spinal condition and uses a wheelchair.

He faces up to life in prison if convicted on the biological-toxin charge. A count of mailing a threat against the president carries up to five years in prison, and five counts of mailing a threat to a U.S. officer are each punishable by up to 10 years.

Allen's trial is scheduled to begin Dec. 26.

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The Associated Press contributed to this report.