The preliminary analysis of the powder shows that it has the same extraordinarily high concentration of deadly spores as the anthrax produced in the US weapons program. The possibility that the anthrax came from a foreign source remains, but the spore concentration is higher than any stock publicly known to have been produced by other governments.
The similarity to the levels achieved by the US military lends support to the idea that someone with ties to the old program may be behind the attacks, which have killed five people.
The FBI recently expanded its investigation of anthrax suspects to include government and contractor laboratories as a possible source of the deadly powder itself, or of knowledge of how to make it.
A yardstick for measuring the quality of
anthrax emerged more than two years ago when William Patrick, a long-time
federal consultant and one of the nation's top experts on biological weapons,
wrote a report assessing the possible risks if terrorists sent anthrax by mail.
Based on the difficulty of developing advanced anthrax, he predicted that the terrorist germs would be one 20th as concentrated as what the government developed and what recently turned letters into munitions.
"The quality of the spores is very good," said a federal science adviser who shared the Patrick report with The New York Times. "This is very high-quality stuff" - equal, he said, in concentration to that produced by the US military before it abandoned germ weapons.
"It's frightening to think that one of our own scientists could have done something like this. But it's definitely possible."
He said the anthrax sent to the Senate contained as many as 1 trillion spores per gram, a figure confirmed by an administration official.
With that concentration, the powder has a vast potential to kill. Estimated conservatively, at 10,000 microscopic spores to a lethal dose, a gram could in theory cause about 100 million deaths.
The letter sent to Tom Daschle, the Senate majority leader, is said to have held two grams of anthrax - enough to make about 200 million lethal doses.
Analysis of the Daschle powder has been hampered by the small amount recovered. That is why investigators are taking great care with the anthrax sent to Senator Patrick Leahy.
The New York Times