Anthrax spores can be used as an effective weapon after they have been dried and milled down to a size of between one and five microns. If the particles are smaller than one micron, they are exhaled. Larger than five microns, and chances are the particles will lodge in the nose.
But administration officials, including homeland security chief Tom Ridge, are not calling the anthrax, which has not shown to be resistant to antibiotics, military grade.
Making such finely-milled anthrax spores requires elaborate machinery, suggesting the powder was produced by a well-funded and possibly state-funded operation.
Federal authorities have also revealed that the anthrax found in Daschle's office came from the same strain as that contained in a letter sent to NBC News headquarters in Manhattan, and the one mailed to AMI.
Ridge has referred to them as "indistinguishable."
An anthrax-tainted letter sent to the New York Post has been sent to an Army facility in Maryland for further testing.
• Thousands of Negative Test Results in N.Y.
At the Trenton Main Post Office in Hamilton Township, N.J., early tests found widespread anthrax contamination, the Associated Press reported. The state epidemiologist reportedly told union members last night that 13 of 23 samples from the building's work areas contained anthrax.
Anthrax-laden letters mailed to the Post, Daschle, and NBC News anchorman Tom Brokaw, were all postmarked from Trenton. Handwriting in the three letters is also similar, the FBI and New York Police Department said in a joint statement.
Like the letter addressed to Brokaw, the Post letter was dated Sept. 18. The letter to Daschle was dated Oct. 8.
The handwritten letters inside the envelopes to Brokaw and Daschle were both dated "09-11-01," the date of the terrorist attacks in New York and Washington, and contained within their messages: "Death to America. Death to Israel. Allah is great."
Federal agents are retracing a postal route in Trenton, and have reportedly seized mailboxes in which someone may have deposited the letters laced with anthrax.
Meanwhile, New York Mayor Rudoph Giuliani said today that numerous tests performed at media organizations in the city had come back negative for evidence of anthrax, including tests of 1,300 employees of NBC News.
Environmental tests at ABCNEWS, where the 7-month-old son of a producer was believed to have contracted the disease, had also returned negative. Investigators have not identified the source of the child's infection, and no suspect letter had been found at ABC.
The number of New Yorkers infected with the anthrax bacteria remains at four, the mayor said, with one case each at NBC, CBS, ABC and the New York Post.
• Anthrax Found in Argentina
Since anthrax was discovered less than a month ago in the United States, scares have occurred around the world. Until this weekend, however, anthrax only had been confirmed outside the U.S. in Kenya.
Now, anthrax-tainted mail has been found in Argentina, a government official there said Saturday. The infected parcel was a travel brochure sent as part of a bulk-mailing from a Miami tourism company to a woman identified only as "Patricia" in a Buenos Aires home, said Hector Lombardo, the nation's health minister, according to the Associated Press.
"There was no exposure," Lombardo said. "The woman is fine because she didn't open the letter."