It's been nearly three months since the first deadly case of anthrax surfaced in Florida. And while much of the attendant hysteria has dissipated, myriad questions have not. Where did the spores come from? Who sent them? Are there more contaminated letters still in circulation? While little is known for sure, the ongoing investigation has yielded some clues as to the bacteria's origin. Meanwhile, health officials are offering some workers a new way to keep anthrax — and, they hope, fear — at bay.

Finding the source

Investigators are just about certain the anthrax that killed five people this fall originated from within the U.S. Domestic terrorism experts have been dispatched to study the patterns and delivery methods of the anthrax letters, hoping to pinpoint some identifying trait linking the attacks to a specific person or group.

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nginx/1.14.0 (Ubuntu) The first order of business is figuring out where the spores came from. That won't be easy. While new tests on letters received by Senators Tom Daschle and Patrick Leahy reveal a genetic fingerprint (called the Ames strain) that's traceable back to the U.S. Army Medical Research Institute of Infectious Disease at Fort Detrick, Maryland, officials point out there are as many as 12 private labs that receive military samples for research. Officials are also checking into an ongoing anthrax-development project at the Army's Dugway Proving Ground in Utah. While the possibility of an Army connection has raised a few eyebrows, investigators are urging people not to jump to any conclusions.

Homeland Security Director Tom Ridge hedged Tuesday when asked specifically about the military's potential involvement in the anthrax attacks. "There are multiple agencies within government that have for many years, for many reasons had access to this strain of anthrax," he told reporters. "The connection [to the military] could very well exist. The fact is we have multiple leads."

According to scientists familiar with the manufacturing of weapons-grade anthrax, the investigation is likely to be frustrating, simply because so many agencies and individuals are familiar with the process, and have access to this specific strain of the bacteria.

Offering a vaccine

Thanks to an historic offer from federal health officials, as many as 3,000 Capitol Hill and post office workers are eligible to receive the anthrax vaccine. This is the first time the government has provided civilians with vaccination against bioterror weapons. (The program is part of an experimental study run by the Centers for Disease Control and Prevention).

The eligible workers are those believed to have been exposed to concentrated anthrax spores; while no new cases have emerged, health officials say they are eager to provide any reassuring measures, out of, as one official put it, "an abundance of caution."

HHS Secretary Tommy Thompson announced the program Tuesday, adding that those not interested in the vaccine (which has been linked to rare but serious side effects) can also opt to take 40 extra days of antibiotics.