A man has been arrested and charged with posting more than 100 threatening letters containing white powder to members of Congress.
Investigators said Christopher Lee Carlson, 39, of Portland Oregon was indicted on two criminal counts.
The letters so far have all tested negative for toxic substances, the U.S. Attorney's office in Portland said.
Carlson was charged with one count of mailing a threatening communication to House Speaker John Boehner.
The second count charged the man with mailing a letter threatening to use a biological weapon to a U.S. senator, Sen. Barbara Mikulski.
Carlson is expected to be arraigned on Monday.
Investigators have recovered more than 100 letters addressed to U.S. senators and representatives. The Seattle office of Sen. Patty Murray, D-Wash., said it also received one.
'Threatening letters - whether hoax or real - are serious concerns that federal law enforcement agencies will aggressively pursue,' said Greg Fowler, special agent in charge of the FBI in Oregon. Read More