(CNN) -- A 39-year-old man was arrested and indicted Friday in connection with dozens of threatening letters containing a powdery substance that were sent recently to congressional offices and members of the media, the Justice Department said.
Christopher Lee Carlson was arrested in his Portland, Oregon-area home, U.S. Capitol Police said. The roughly 100 threatening letters -- none of which tested positive for toxic substances -- were postmarked in Portland, according to authorities.
Carlson faces charges of mailing a threatening communication to a member of Congress and mailing a letter threatening to use a biological weapon to a U.S. senator. He is to be arraigned Monday.
Members of Congress who received some of the letters included House Speaker John Boehner, R-Ohio, and Sen. Barbara Mikulski, D-Maryland, according to the indictment.
Senate Sergeant at Arms Terrance Gainer applauded the news of the arrest, calling the joint operation "the result of outstanding investigative work and textbook cooperation among federal, state and local law enforcement."
While phone and letter threats to congressional offices are relatively common, precautions against a possible toxic chemical attack increased after letters containing anthrax sent to congressional offices and news organizations killed five people and sickened 17 others in 2001.
CNN's Chandler Friedman and Deirdre Walsh contributed to this report.