A man was arrested at a Portland, Ore.-area home in connection with white powder letters sent to members of Congress, according to U.S. Capitol Police.
Christopher Lee Carlson, 39, faces charges related to mailing threatening communication and threatening the use of a biological weapon.
Several letters containing suspicious substances were sent to U.S. senators and representatives in recent weeks. Each tested negative for toxins.
Suspicious letters also have been mailed to other locations across the country recently, including seven received in D.C. this week.
Capitol Police cooperated with the U.S. Postal Inspection Service, the FBI and local law enforcement agencies in the investigation.
"As soon as the first suspicious letters were received, they worked tirelessly to identify the suspect and bring him into custody," Senate Sergeant at Arms Terrance Gainer wrote in a letter to the Senate community.