There is now word that someone tried to send a letter to the White House laced with the lethal poison ricin. The incident occurred in November and was kept quiet for months.
The letter was intercepted at a mail handling facility off the White House grounds and never reached its intended destination.
Law enforcement sources say it contained a fine powdery substance that later tested positive for ricin. They say it was low potency and was not considered a health risk.
The news emerged as an investigation continued into traces of ricin found Monday in a U.S. Senate office building. The substance showed up in the mailroom of Senate Majority Leader Bill Frist's office.
Senator Frist, who is also a doctor, says there are no signs anyone who was near the contaminated area has developed any medical problems. The three main Senate office building have all been closed, but Congress remains in session.