A Navy veteran in Utah has been charged with threatening to use a biological toxin as a weapon by sending letters to President Donald Trump and other leaders containing ground castor beans, the substance from which ricin is derived.

Charging documents filed earlier this month in U.S. District Court say 39-year-old William Clyde Allen III told investigators he wanted to "send a message," though he did not elaborate.

The indictment alleges he knowingly threatened to use a biological agent and toxin, specifically ricin, as a weapon — a charge for which he could face life in prison if convicted.

Allen is also charged with one count of mailing a threat against the president and five counts of mailing threatening communications to an officer or an employee of the United States.

He has pleaded not guilty, according to an Oct. 18 statement from the U.S. Department of Justice.

Authorities say the envelopes were mailed to Trump, FBI Director Christopher Wray, CIA Director Gina Haspel, Defence Secretary Jim Mattis, the Navy's top officer, Adm. John Richardson and Secretary of the Air Force Heather Wilson. . Some allegedly had Allen's return address.

Authorities have said the letters were intercepted and no one was injured. Castor beans can cause injury if swallowed, according to the Centers for Disease Control and Prevention.

Allen served in the Navy from 1998 to 2002, according to Navy records. He has a criminal record in Utah including child abuse and attempted aggravated assault, including to court documents filed on Thursday.

Last year, he sent a vague email threat to the Air Force, said Logan, Utah police Capt. Tyson Budge, though military officials did not believe he was capable of carrying it out.

Another letter sent to Utah Gov. Gary Herbert in July blamed him for health problems Allen's wife was suffering, Budge said.