PORTLAND, Ore. (AP) - A 39-year-old man was arrested Friday in connection with threatening letters containing a suspicious powdery substance that were sent to members of Congress.

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The United States Capitol Police said in a statement that Christopher Lee Carlson was arrested at a home in the Portland, Ore., area. No further detail about where the home was located was immediately available.

Authorities say Carlson faces charges related to the mailing of a threatening communication and threatened use of a biological weapon.

This arrest was the result of a joint investigation between the U.S. Capitol Police, the FBI, and the U.S. Postal Inspection Service. Over the past few weeks, these agencies recovered a number of threatening letters sent to U.S. senators and representatives.

The letters tested negative for toxic substances.

The letters, which were also sent to several media organizations, told the recipients that there is a "10 percent chance you have just been exposed to a lethal pathogen."

The letters bore a return address from "The MIB" and were postmarked Portland. The Portland return address on the letters appeared to be phony.

The sender wanted an "end to corporate money and 'lobbying,'" an end to corporate "personhood" and a new constitutional convention. The Associated Press obtained a copy of a letter.

The threats raised memories of post-9/11 incidents that rattled Washington. In mid-November 2001, authorities closed two Senate office buildings after anthrax attacks on Congress. Those attacks came after four people - two postal workers in Washington, a New York City hospital worker and a Florida