Matthew Buquet, 37, entered not guilty pleas during an appearance before U.S. Magistrate Cynthia Imbrogno.
He is charged with producing and transferring a biological toxin called ricin; mailing a threatening communication to the president of the United States; and mailing a threatening communication to a federal judge. He faces up to life in prison if convicted.
Buquet has waived a bail hearing in the case and remains in the Spokane County Jail.
The FBI has said Buquet mailed five ricin-laced letters to various federal entities. He was arrested last month. All the letters have been recovered and there were no reports of injuries.
No motive has been offered for the mailings, and the federal government has sealed most of the court documents in the case.
Little is known about Buquet, who has made no statements in court other than "yes" or "no" answers to questions from the magistrate. He appeared in court Wednesday with a long black beard, dark-tinted glasses and wearing shackles.
A grand jury indictment issued last week contended that Buquet developed the biological agent in violation of federal law, and that he mailed letters containing ricin to Obama and U.S. District Court Judge Fred Van Sickle of Spokane.
The letters also contained the statement: "We have a bomb placed. We are going to Kill you. Hezbollah," according to the indictment.
The other letters were mailed to a Spokane post office, Fairchild Air Force Base and the CIA.
Buquet most recently worked as a janitor, and was a registered sex offender who lived in a rundown apartment building near downtown Spokane.
A search of public records showed Buquet doesn't appear to have any close relatives in the U.S.
A Facebook page with his name and photo said he was originally from Bogota, Colombia, and studied electronic engineering technology at ITT Technical Institute in Spokane Valley.
Ricin is a highly toxic substance made from castor beans. As little as 500 micrograms, the size of the head of a pin, can kill an adult if inhaled or ingested. The recipe for making the poison is readily available on the Internet.
The FBI has said the Spokane investigation is not believed to be connected to an earlier case in which letters containing ricin were addressed to President Obama, a U.S. senator and a Mississippi judge. A Mississippi man was arrested in that case.
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