As federal investigators try to trace the origin of suspected ricin found Monday in the office of Senate Majority Leader Bill Frist, ABCNEWS has learned of an earlier, undisclosed incident in which a ricin-laced letter was intercepted on its way to the White House.
In November, a letter postmarked Chattanooga, Tenn., and addressed to the White House was intercepted at an off-site mail sorting facility in the Washington area, sources told ABCNEWS.
The powdery substance in the letter tested positive for ricin. However, the tests indicated that the poison was in a low-potency, granular form that posed no health risk, the sources said.
According to two law enforcement sources, the intercepted letter addressed to the White House was signed "Fallen Angel."
That sign-off was also used in a letter that was part of a package containing ricin that was left at a post office in Greenville, S.C., in October 2003.
That letter complained about new federal trucking regulations requiring more rest for drivers. The letter described the author as "a fleet owner of a tanker company" and contained this threat: "If my demand is dismissed I'm capable of making Ricin … I will start dumping."
The Greenville package contained a small metal vial packed with ricin. The FBI has offered a reward of up to $100,000 for information leading to an arrest in the incident. No illnesses were reported in the Greenville case and an FBI spokesman in Columbia, S.C., said the sender's motivation may not have been to kill.
"When you use a poison like ricin you obviously have to be concerned that it could kill, but if you look at the language in the letter, it seems that this individual was more concerned with seeking a repeal of the new legislation," said the spokesman, Tom O'Neal.
Late on Monday, authorities discovered a suspicious powder in the Dirksen Senate Office Building.
A number of tests have identified the substance as ricin, a potentially deadly poison derived from castor beans, although final confirmation is still under way. Government health officials hope to have those results Wednesday.
Federal investigators are trying to establish whether the Senate incident is connected to the two earlier packages.