As the number of anthrax cases continues to grow, involving states from Florida to New York to Nevada, the lack of a clear connection between them has left officials unsure of what to look for - and left many Americans eyeing their mail with a new level of suspicion.
While all three cases seem to involve letters sent through the mail to major corporations - two to media organizations and one to a Microsoft branch - they originated from different sources and reportedly had different contents, leaving authorities struggling to find a common thread that links them to each other, or to the Sept. 11 attacks.
Many terrorism experts say the incidents don't exactly fit the profile of Osama bin Laden and the Al Qaeda network, since the letters have targeted such small numbers of people, and have so far only succeeded in killing one.
A more likely scenario, several suggest, might be a bioterrorist version of the Unabomber, with the Sept. 11 attacks acting as a kind of catalyst. More than one individual or group could be involved.
Yet Attorney General John Ashcroft said yesterday he is not ruling out a connection with Al Qaeda. "We should consider this potential that it is linked" to bin Laden.
Whoever is responsible for the anthrax attacks has certainly achieved a primary goal of Mr. bin Laden's group - to disrupt American society as much as possible. Although only a tiny number of people have been exposed to the disease, pharmacies across the US are selling out of Cipro, the drug used to treat anthrax, and hospitals and emergency rooms have had to deal with large numbers of people demanding to be tested.
Likewise, law enforcement and public health officials have seen their resources stretched thin as they struggle to respond to a full range of potential threats, the vast majority of which have turned out to be hoaxes.
"That's going to be the hard part from here on out - what do you take seriously, and how do you separate the wheat from the chaff?" says Amy Smithson, director of the Chemical and Biological Weapons Nonproliferation Project at the Henry L. Stimson center in Washington. "Nobody will want to just assume it's a hoax."
The different circumstances surrounding each anthrax episode so far has made it difficult for officials to establish a clear pattern or framework within which to view them.
The letter that infected one and possibly two NBC News employees in New York contained an unspecified threat to anchor Tom Brokaw, and was postmarked from Trenton, N.J. The one sent to a Microsoft branch in Reno, Nev., came from Malaysia and contained pornographic clippings.
Before the New Jersey letter tested positive, speculation had focused on another piece of mail sent to NBC that contained a white powder and matched one sent to a New York Times reporter. Both of those letters tested negative, however.
In the original case involving the offices of American Media in Boca Raton, Fla., the source of the anthrax has not yet been identified. Speculation has focused on a letter that reportedly contained a Star of David and a bluish powder. At least eight employees there have now tested positive for exposure to anthrax, including the one who died.
The mere presence of letters, along with the limited nature of the attacks, leads some analysts to believe Al Qaeda may not be responsible.
Bin Laden "likes big, very dramatic events," says Jason Pate, manager of the Weapons of Mass Destruction Terrorism Project at the Monterey Institute in California. "Yes, there's a lot of media attention on the anthrax cases, and it has a very ominous, sinister effect psychologically. But it doesn't quite have the boom that has been Al Qaeda's m.o. for the past three years."
Given that bin Laden's goal seems to be to hurt as many people as possible, "I don't think they would write letters," he adds. "There would be no letters - and people would [mysteriously] be coming down with anthrax."
Experts point out that in the past few years, there have been hundreds of hoaxes involving anthrax across the country - and that these recent outbreaks might indicate that one of those groups had finally succeeded in carrying out its threat.
It's also quite possible that an event like Sept. 11 would lead to copycat crimes.
These have occurred regularly after major public health scares in the past, such as the Tylenol poisoning in 1982, says Mr. Pate.
Still, even if the incidents don't seem to fit with the typical Al Qaeda profile, the group itself is so loosely defined that it is hard to make any assumptions about its operatives. For example, there could be a bioterrorist subset of Al Qaeda that's only loosely affiliated with the organization, Pate suggests.
For authorities, a main focus now will be to analyze the anthrax samples to try to find out what strain was used, and perhaps ultimately trace them back to a production facility.
The process of growing anthrax leaves certain identifying markers, says Randall Larsen, director of the ANSER Institute for Homeland Security, a nonprofit group in Arlington, Va. "It's kind of like a great detective story. You get a fingerprint here, a thumbprint there, a couple marks on the bullet," he says. "We may eventually get a return address on where this was manufactured."
In the meantime, he says, Americans should not be afraid to open their mail. And if they do come across a suspicious package containing some sort of powder, they should just carefully put it in a trash can, tie the bag tightly, and call the authorities.
"By putting it in that plastic bag and tying a knot, it's no longer a weapon," says Mr. Larsen. "It's just trash."