WASHINGTON - The ricin sent to top government agencies - including the White House - is probably coming from inside the United States and from a homegrown criminal rather than foreign terrorists, investigators and outside experts said they believe.
"It does not bear the mark of an international terrorist attack," said an official at the Department of Homeland Security yesterday, speaking on the condition of anonymity.
"This is a criminal issue. It is not a weapon of mass destruction," the official said.
Meanwhile, the investigation has broadened beyond Washington to Chattanooga, Tenn.
Senate Majority Leader Bill Frist, a Tennessee Republican, said late yesterday that tests are being conducted at a postal facility there for the presence of ricin.
He declined to elaborate.
Others, who wouldn't be quoted by name, hinted of fears of possible contamination from processing one of the letters.
Ricin-tainted letters sent in the fall were signed "Fallen Angel," a self-described U.S. business owner who had a gripe against a Department of Transportation rule that increased the amount of sleep required for truckers.
Investigators are trying to determine whether ricin found Monday in Frist's mailroom is connected to those earlier letters.
Hampering the investigation is the fact that no letter or package that contained the powdery ricin has been found.
White House spokesman Scott McClellan acknowledged yesterday that a ricin-laced letter was sent to the White House but intercepted in an off-site mail facility in November.
"The letter was deemed by public health officials not to be a public health threat," he said, so the White House kept its existence a secret to aid investigators.
The first "Fallen Angel" letter was addressed to the Department of Transportation and found in a Greenville, S.C., post office Oct. 15.
The author threatened to start "dumping" the poison if the trucking rule, which went into effect Jan. 4, wasn't stopped.
Ricin, a toxin that causes cell and organ failure, is made from easy-to-find castor beans, but experts say that, unlike anthrax, it can't cause mass casualties.
"It's not a big threat. It's the equivalent of mailing rat poison to somebody," said Randall Larsen, founder of Homeland Security Associates, a consulting firm in Alexandria, Va.
"This fits in the category of kook rather than terrorist," Larsen said.
The FBI, which handles criminal cases, is the lead agency investigating all three letters.
Federal officials, however, gave somewhat conflicting accounts of the ricin-tainted letter sent to the White House in November, which was first revealed late Tuesday.
Secret Service spokeswoman Ann Roman said the letter was received by the White House mail-sorting office Nov. 6, opened and tested because of its contents.
Initial tests showed no ricin.
But the postal mail-sorting machinery tested positive the next day.
Federal authorities were notified Nov. 12, she said.
The ricin was confirmed locally Nov. 13, and samples were sent Nov. 14 to the Centers for Disease Control and Prevention in Atlanta and also confirmed, Roman said.
She said the CDC also found that the substance was of low potency and of no risk to public health.
But CDC spokesman Tom Skinner said the CDC tested only for the presence of ricin, not potency, and determined that there was no health threat based on "information that was provided to CDC."
Postal Service spokesman Gerry McKiernan said his agency was told two days before the CDC tests that "there was no evident health threat, which put our minds at ease."
The White House's admission yesterday that it kept its ricin letter a secret was both criticized and praised by experts on crime.
Keeping the threat quiet might cause the ricin sender to "strike out even more," said Jack Kataeff, an Alexandria, Va., forensic psychologist who specializes in criminal behavior.
In contrast, Gary Aumiller, the president of the Society of Police and Criminal Psychology, said: "Terrorism is a psychological war. ... If they don't get the publicity, they're not winning their battle."
Senators and their staffs will be allowed to return today to the Russell office building.
The Hart office building will open tomorrow.
The Dirksen office building, where the ricin was discovered, is slated to reopen Monday.