Al Qaeda's Anthrax
Is Osama
bin Laden behind the mail attacks?
by Richard A.
Muller
Technology for
Presidents
April 16, 2002
October 5 may
not be as famous as September 11, but it may prove more historic and seminal. On
that day last year the United States suffered its first death ever from a
biological warfare attack. Over the following two months, 21 additional people
were infected with anthrax, and four of them died. We don't know who planned
the attack or who perpetrated it, where they obtained the anthrax or why it was
done. The delivery weapon was the U.S. mail, although even that isn't certain
for all the deaths. The World Trade Center attacks are clear and
well-understood, compared to the anthrax mystery.
Although the
evidence remains circumstantial, most experts continue to believe that the
anthrax terrorist was a disgruntled U.S. citizen, working alone, trying to
frighten and kill, or perhaps to probe our biological warfare defenses. Much
of this theory is based on handwriting analysis of the anthrax letters, along
with
reports that the anthrax was the American Ames strain, apparently refined for
military use. Barbara Rosenberg of the Federation of American Scientists gives
an extensive review of the data (see her Analysis
of the Anthrax Attacks at the FAS website), and argues that the FBI knows the identity of the perpetrator
but is keeping it secret, perhaps to protect classified programs.
I disagree
with these experts. Judging from such factors as the timing of the anthrax
mailings, the delivery method, the quantity of spores used and the information
that was publicly available about anthrax's lethality, I think it likely that
the anthrax terrorists were working for Osama bin Laden, and intended to murder
thousands of people. In other words, the letters were the main salient of the
"second wave" of al Qaeda terrorism. Many political questions cloud
the issueÑfor example, why bin Laden would want to target Senate Democrats. I'd
like to set those aside for a moment and explain the scientific reasoning
behind my view. My hypothesis may not be widely shared, but unless we consider
it seriously, we risk overlooking many productive trails toward a solution of
the anthrax mystery.
First, look at
the delivery method. A study posted on the Web by the Defence Research
Establishment Suffield in Alberta, Canada on September 1Ñwell before the
anthrax letters were mailed-suggested that envelope-borne anthrax spores could
be aerosolized very effectively by the simple act of opening the mail. The
report stated that anthrax dispersal from letters was "far more effective
than initially suspected"; greater than 99% of the respirable aerosol
particles in an envelope were released into the air when test envelopes were
opened. (Steven Block of Stanford alerted me to this site.) The report
concludes that lethal doses can spread rapidly throughout a room where an
anthrax-laden envelope is opened. Any terrorist checking the Web in early
September might have found this report and decided to act on it.
Next, consider
the amounts of anthrax used. Other data in the public domain suggested that
even a few grams of anthrax could, if dispersed with perfect efficiency, kill
millions of people. Any terrorist who put this information together with the
Canadian study might have concluded that the post was an ideal way to kill a
building-full or even a city-full of civilians. If this is true, then the
attack was not to be a demonstration; it was not planned to disrupt the mail,
or even the U.S. economy. It was intended to commit mass murder, including
United States leaders and media personalities.
If mass
anthrax deaths were part of the perpetrators' plan, how did it go so wrong? I
suspect that the terrorists were influenced by the misleading technical concept
of "lethal dose." Consider the following paradox: Senator Patrick
Leahy, after a briefing on the possible contents of the letter sent to him,
announced on Meet the Press that it might contain "100,000 lethal
doses." Yet only five people died from all the letters. Was Leahy exaggerating?
No. He was being conservative.
How can we
reconcile five with 100,000? Based on primate experiments, the Defense
Intelligence Agency estimates that 2,500 to 55,000 spores are enough to trigger
fatal pulmonary anthrax infections in half of those exposed (the dose
epidemiologists call "LD50"). It is possible that any one spore can
trigger the disease, but the probability is low, so many are required, on
average. Ninety-four-year-old Ottilie Lundgren, the fifth and last victim, may
have been killed by just a few spores. That would explain the absence of
detectable anthrax in her home and belongings.
To penetrate
into the most sensitive areas of the lungs, the spores or clumps of spores must
be small, with diameter not much larger than three microns and a weight of
about 10 picograms. Leahy's letter was reported to contain two grams of finely
divided anthrax, 200 billion such particles. If we assume 10,000 particles is a
reasonable average for LD50, then the letter contained 20 million lethal doses.
So Leahy's estimate of 100,000 was actually low.
In the
worst-case scenario (or the best-case-from the terrorist's point of view), the
anthrax spores sprinkle out of an envelope, disperse like dust, are swept up
into a building's ventilation system and get mixed and uniformly diluted in the
recirculating air. A human breathes about a cubic meter of air every hour. With
10,000 particles in each cubic meter, two hundred billion particles from one
letter could (in principle) contaminate 20 million cubic meters, almost the
volume of the entire New York City subway system.
This
worst-case scenario, however, is highly misleading. The primary challenge in
the military use of anthrax has always been to find methods to mix the spores
thoroughly with the air, and keep them there long enough to be breathed. Most
dispersal methods are extremely inefficient. Lethal doses, per se, aren't
meaningful.
I suspect the
terrorists didn't appreciate this. In my scenario, they had managed to obtain a
few grams of spores, perhaps stolen from a U.S. research facility. They
correctly estimated that they had several hundred million lethal doses. Even at
only 1% efficiency (a conservative estimate, they mistakenly thought), they
could kill 2 million Americans. Of course, the lethality might be limited to
one building, and maybe some surrounding area, so only thousands would dieÑor
only hundreds, if they were very unlucky.
But their
initial anthrax attack was a disappointing failure; only one person died,
Robert Stevens, a photo editor at the Sun, a tabloid newspaper. The Canadian test, thankfully, may
not have been good predictor of anthrax spores' behavior in the real world. In
that study, the anthrax was folded in a contained sheet and was ejected when
the sheet was pulled and opened. Perhaps the terrorists just dropped the
anthrax into the envelope, where it remained. It is also possible that the
anthrax had migrated out of the sheets during the extensive handling by the
post office and settled to the bottom. And finally, maybe the anthrax did
disperse, but only through the rooms where the letters were opened; the
Canadian tests did not include measures of dispersal through ventilation, and
this kind of dispersal may not be so efficient. In the tests, the half-life of
the anthrax exposure in the chamber was about five minutes, suggesting that it
settles quickly. (The air in the test chamber was recirculated, so the loss
wasn't through dilution.) Five minutes is long enough to infect people in the
room, but not for spores to migrate far.
At this point,
I believe, the U.S.-based al Qaeda agents panicked. They had failed in their
mission, and they didn't know why. They guessed that their anthrax had lost its
potency, and in desperation, they mailed out all of the remainder, much of it
in pure undiluted form, on October 9.
Anthrax spores
were eventually detected not only at the U.S. Senate and the House of
Representatives, but also at the White House mail facility, the Supreme Court,
the CIA mail facility, the Pentagon, and all over Washington, DC. The
prevailing belief is that spores spread to so many sites through
cross-contamination in the mail rooms. But I think it worthwhile to consider
the possibility that some of the detections were from early, diluted letters.
In their first mailings, the terrorists assumed the anthrax could be diluted,
and spread in this way to more locations. This may also account for several of
the "hoax" letters that Rosenberg describes.
My scenario may
seem complex, but real scenarios always are. I don't claim to have the details
correct. No scenario presently explains everything, and to make sense of the
complex situation, you must judge your evidence. Which is more credible when
the conclusions conflict: a handwriting analyst who says the terrorist was
American, or a medical doctor, Dr. Christos Tsonas, who had treated the leg of
Ahmed Alhaznawi, one of the September 11 hijackers, and says "the most
probable and coherent interpretation of the data available" is that the
infection was skin anthrax? If we are searching only for an American who could
have mailed the anthrax, we might miss the American who didn't mail it, but did
steal itÑor maybe just failed to destroy it, when ordered to do so.
My opinion is
in the minorityÑin fact, the tiny minority. According to the October 27 Washington
Post, a senior
official said "nobody" believes the anthrax attack was the second
wave. "There is no intelligence on it and it does not fit any [al Qaeda]
pattern." But whether it fits the al Qaeda pattern depends, in part, on
the intended scale of the carnage. It may be a mistake to assume the attack
worked out as planned.
If I am right, the terrorists may now be disillusioned with anthrax attacks. But it would be foolish to relax. Bin Laden was building laboratories in Afghanistan that, given time, could have produced not grams but kilograms of spores. Tons of anthrax were grown in Soviet laboratories, and buried on Vozrozhdeniye Island in the Aral Sea (just north of Iran and Afghanistan)Ñpossibly along with some smallpox virus. (It was treated with bleach, but tests show much of it is still viable.) The Soviet anthrax was reported to be resistant to most antibiotics. So, despite the limited casualties of this first biological warfare attack on the United States, the prognosis is bleak. Biological terror is likely to prove more accessible and easier to implement than nuclear terror. The "mad scientist" of future fears is more likely to be a biologist than a physicist. Even though I am a physicist, that thought does not give me much comfort.
(Still not convinced?
See a subsequent article
by David Tell that makes a similar case.