Suspect in Congress mail threats pleads not guilty to added charges

A registered nurse from Portland, Oregon, entered a not guilty plea on Thursday to additional charges relating to more than 100 threatening letters he allegedly mailed to members of Congress in February.

Christopher Carlson has been jailed without bond since his March 9 arrest for allegedly mass mailing envelopes from Portland that contained a suspicious white powder. The powder, later found to be harmless, triggered security alerts on Capitol Hill and among several media outlets, Reuters reports.

The 10 additional felony counts against Carlson were contained in an expanded indictment returned on March 28 by a federal grand jury. The charges came after Carlson entered not guilty pleas to two earlier charges. He pleaded not guilty to 12 charges - six counts of mailing a threat to use a biological weapon and six counts of mailing a threatening communication to a member of Congress.

If Carlson is convicted, he could face a maximum penalty of 90 years in prison. More than 100 threatening letters were received by various media offices and lawmakers, including National Public Radio and House of Representatives Speaker John Boehner. Authorities have yet to offer a possible motive, according to Reuters.

A trial date is currently set for June 5. The security alert in February was the largest postal scare in Washington, D.C. since deadly anthrax-containing letters were sent to several Senate offices and news organizations in 2001. Seventeen people were sickened by the letters and five were killed.