Investigators also want to determine whether the incident is linked to similarly contaminated letters apparently found last fall at mail facilities serving the White House and a South Carolina airport.
Capitol Police Chief Terrance Gainer said the FBI and the Joint Terrorism Task Force launched a criminal investigation after the powdery white substance was found Monday on a machine that opens mail in Senate Majority Leader Bill Frist’s office in the Dirksen Senate building.
Subsequent tests determined that the powder was ricin, a potentially fatal toxin with no antidote, although testing was ongoing to determine whether it was sufficiently potent and in a powder fine enough to kill people.
“We have an open mind about the source of this,” said Gainer.
Separately, law enforcement sources told news agencies Tuesday a letter containing ricin and addressed to the White House had been intercepted last November but the finding had not been made public as it was not considered a public health risk.
A letter with ricin was also found in October at a South Carolina postal facility serving the Greenville-Spartanburg International Airport, according to media reports.
Both letters were signed by someone who called himself “Fallen Angel” and complained about new trucking regulations.
White House spokesman Scott McClellan said President Bush was not told about the ricin letter sent to the White House and defended the absence of a public disclosure of the incident because “it did not pose a public health risk.”
“We share information appropriately, if there is a public health risk,” said McClellan, according to the Associated Press.
Tennessee Republican Frist, a physician, said it was encouraging that no one on Capitol Hill had shown signs of illness nearly 24 hours after Monday’s possible exposure. “I’m happy to report everybody is doing fine,” he said. “Usually injuries occur in the first four to eight hours.”
The area where the poison was found was quarantined and stacks of mail were being checked throughout the Capitol complex.
The incident evoked memories of the letters sent to the Senate and news media offices in 2001 that were laced with anthrax. Five people died and 17 were injured in that attack, which the FBI is still investigating.
Three Senate office buildings were closed Tuesday. They were to remain closed Wednesday and all Capitol tours were canceled.
Frist said he hoped the offices would be opened by next week. Lawmakers continued business on the Senate floor in the Capitol building, and the House of Representatives remained opened.