The operatives and allies of Al Qaeda have something in mind for the United States, of that there can be little doubt. Something nasty. Vice President Dick Cheney said in May it is "almost certain" that the terrorists will strike again. Defense Secretary Donald Rumsfeld warned that terrorists "inevitably" will get their hands on weapons of mass destruction, "and they would not hesitate one minute to use them." Question: What if they already did use them and are preparing to do so again? Were last year's anthrax attacks, which caused five fatalities, a preview?

No one knows, of course. That said, there are dots worth connecting.

The perpetrator(s). In November, the FBI issued a suspect profile identifying the likely anthrax attacker as a single adult male, probably an American with a scientific background, lab experience, poor social skills, and a grudge. Some people -- I was one of them -- viewed this interpretation with skepticism. What would be the motive? Why the timing so close to September 11? A number of analysts, including David Tell in a useful article in The Weekly Standard on April 29, have subsequently cast doubt on the disgruntled-scientist hypothesis, and an FBI spokesman said in May that the bureau, far from being "convinced" that the attacks were carried out by an American loner, had "not precluded any category of suspect, motive, or theory."

If anything, hints that anthrax and Al Qaeda may be linked have grown harder to dismiss. Dot one: Several of the hijackers, including their suspected ringleader, Mohamed Atta, are reported to have looked at crop dusters in Belle Glade, Fla. Dot two: Among five targeted media organizations, only one was not nationally prominent -- American Media, of Boca Raton, Fla., which happens to be a few miles from where Atta and other terrorists lived and attended flight school. (Atta rented an apartment from a real estate agent whose husband worked for American Media.) Dot three: In March a doctor in Fort Lauderdale announced that he had treated one of the terrorists for what, in retrospect, he believes was cutaneous anthrax. Doctors at Johns Hopkins University examined the case and concurred that anthrax was "the most probable and coherent interpretation of the data available."

Other recent reports cite captured documents and an unfinished lab in Afghanistan that suggest Al Qaeda was interested -- as presumably it would be -- in producing biological weapons, including anthrax. In 1999, an Arabic-language newspaper in London reported that "elements loyal to [Osama] bin Laden" had, for a few thousand dollars, "managed to obtain an offer for the supply of samples of anthrax and other poisons" from a former Soviet bloc country.

None of that proves anything. The FBI checked the 9/11 terrorists' homes, cars, and personal effects for anthrax. "Exhaustive testing did not support that anthrax was present anywhere the hijackers had been," an FBI spokesman told The New York Times in March.

A point worth noting: The anthrax-laced letters were all mailed after the deaths of Atta and his fellow hijackers. If Al Qaeda did have something to do with the anthrax attacks, whoever did the mailings is still out there.

The material. In April, news reports said that the material used in the attacks was not only "weaponized" but also more sophisticated than anything that U.S. military labs had managed to produce. In May, other news reports said that the material was (in The Times' words) "far less than weapons grade." Good grief. What's the story?

Everyone agrees that all of the anthrax was of the same type, known as the Ames strain. Most sources also agree that the first mailing, to the media organizations, contained a cruder formulation than the second, to Sens. Thomas A. Daschle, D-S.D., and Patrick Leahy, D-Vt. They also concur that the second batch was of impressive purity and concentration. "Very, very pure" is how Matthew Meselson, a Harvard University biologist who has looked at images of the material, described it in an interview. "If you look at it under the electron microscope, you don't see anything but anthrax spores." A cruder preparation, by contrast, would contain so-called vegetative cells and other debris.

One source of ultra-pure anthrax might be a foreign bio-weapons program. An obvious suspect: the former Soviet Union. The Soviets had as many as 2,000 scientists working on anthrax, Tell writes. In 1979, dozens, or hundreds, of Russians died when anthrax leaked from a bio-weapons facility in Sverdlovsk. Subsequent analyses found four or more different anthrax strains in tissue samples taken from the victims.

So does the material used in America last year look Soviet? No, says Ken Alibek, a former Soviet bio-weapons official who is now executive director of the George Mason University Center for Biodefense. He has reviewed images of the material and says it looks like nothing he saw in the Soviet Union. The material, in fact, is of mediocre quality, he told me, and was not produced industrially. It definitely had not been milled, nor did it appear to have any sort of coating to reduce static or otherwise enhance its deadliness. Silica supposedly found in the material, Alibek thinks, may simply be a residue from an unsophisticated drying process. Meselson concurs that the anthrax evinces no sign of special coating or processing. "There is no evidence that I know of," he told me, "that it was treated in any special way."

What about Iraq? It is known to have produced several thousand gallons of anthrax, but that was in liquid form. Stephen D. Bryen, who headed the Pentagon's Defense Technology Security Administration during the Reagan administration and who now is the managing partner of Aurora Defense, says that United Nations inspectors in Iraq found no "dusty" anthrax (the dry, wafting variety used in the U.S. attacks) -- which of course could mean either that the Iraqis didn't (yet) have it or that they hid it well. Bryen also notes that the Iraqis, like the Soviets, tend to mix together various germs (or strains) and chemicals in their weapons, presumably to defeat countermeasures. The U.S. anthrax was all of a single strain.

If the U.S. anthrax was very pure but not specially weaponized, could it have been made by amateurs? In small quantities, yes, according to both Alibek and Meselson. It could be done, Alibek says, with "a very simple, nonindustrial process -- a very primitive process -- that could let you get a trillion spores in one gram. You can't make hundreds of kilos, but you could make hundreds of grams at this concentration."

Meselson concurs. "It's something that could be done by a fair number of people." The necessary glassware, culturing media, centrifuges, and so on "would exist in a large number of places, both hospitals and laboratories -- widespread."

The U.S. attacks, Meselson notes, confirmed what a Canadian simulation had already shown: Even uncoated, nonindustrial-grade anthrax easily suspends itself in the air, floating around and penetrating lungs. No special coating or treatment is necessary. Whoever produced the few grams used last year could presumably produce more. Not enough to fill a crop duster, perhaps, but enough to kill a lot of people.

The outlook. So what to assume? Bryen notes that dropping anthrax in the mail was a very primitive way to distribute it. "It's not how regimes think about dispersing a biological or chemical weapon," he said. "Which should say that the guy distributing it was a total amateur." That, in turn, argues for what Bryen calls the "sample" theory. "The sample theory being that somebody gave these guys a small amount. It has all the characteristics that it was given to people who didn't have any idea how to use it."

Or maybe, on the other hand, not. Paul Ewald, a biologist at Amherst College and the author of Plague Time: The New Germ Theory of Disease, suggests that inefficient distribution might have been exactly the point. "If this attack was caused by the Al Qaeda group -- and I think that's the best explanation, given the evidence available -- this small release would be most useful as a demonstration that they have anthrax on U.S. soil."

If the terrorists are dumb, Ewald says, they made or obtained a few grams of anthrax and mailed off their whole supply. "We'd be wiser if we planned for the smart-terrorist possibility," he says. Smart terrorists would have made or obtained larger quantities of the stuff and stashed it, probably (if they're smart) before setting off alarms by sending out a few grams. Later, with the potency of their weapon proved, they could mount, or threaten to mount, a much larger attack.

Ewald argues for a policy that assumes this is what's going on and that urgently enlists the public's eyes and ears and memories. "We should be alerting people to let authorities know of any suspicious activity they may have seen that would relate to people hiding canisters or objects or doing something that didn't look right," Ewald says. The question is not whether Ewald is right, but whether we want to bet he is wrong.