by William J. Broad and David Johnston, New York Times
Deepening the mystery of the biological attacks that terrified the nation
last fall, federal investigators have discovered that the anthrax sent
through the mail, in general, grew more potent from one letter to the next,
with the spores in the final letter to be opened the one sent to
Senator Patrick J. Leahy of Vermont the deadliest of all.
The finding has surprised and worried investigators, who say it poses
new riddle: was the culprit an amateur making gradual improvements through
experimentation, a malevolent professional intentionally ratcheting up the
potency of the germ powder, or someone else entirely?
It also suggests that after more than six months of painstaking effort,
government experts investigating the anthrax strikes are still at sea. Part
of the problem, they admit, is a lack of advisers skilled in the subtleties
of germ weapons.
The discovery of the progressive potential deadliness of the anthrax
the latest conclusion of scientific testing that investigators are hoping
will help crack a case that has baffled the F.B.I. since the first anthrax
fatality: that of Robert Stevens, a photo editor at a Florida supermarket
tabloid, who died on Oct. 5.
With five anthrax deaths linked to the contaminated mailings, the F.B.I.
inquiry has consumed millions of hours of interviews, neighborhood sweeps
and other detective work. For example, F.B.I. laboratory analysts matched
the serrated ends of the strips of cellophane tape used to seal the anthrax
letters. That meant that whoever sealed the letters, without leaving any
fingerprints, tore off successive strips of tape from the same roll,
But investigators acknowledge that they still have no idea who is behind
the tainted letters. So they are increasingly turning to science to unravel
the mystery. Tests being conducted at several private laboratories may
reveal the precise biological signature of the anthrax used in the mailings,
helping to narrow the search for the laboratory from which it came.
Analyses of the anthrax sample and the chemicals used to coat it could
leave telltale clues to the techniques and equipment used to manufacture
Investigators previously believed that the anthrax sent to Mr. Leahy,
Democrat who is chairman of the Senate Judiciary Committee, and Tom Daschle,
the Senate majority leader, were identical in strength. Each letter was
mailed from Trenton on Oct. 9, 2001. Each had the same photocopied message
But it turns out that the Leahy anthrax is finer, its spores having a
smaller range of particle sizes, officials familiar with the federal
"It could be that the final steps of the processing were done in steps,"
a senior government official said. "You take it so far, and take off a
bunch. You go further, and take off another bunch."
Despite the increasing sophistication of the anthrax, investigators say
they still judge that the deadly powder could have been made in any of
thousands of biological laboratories, though getting the right starter germs
would have been difficult.
An aide to Senator Daschle opened the letter on Oct. 15, and officials
quickly warned that its anthrax was of high quality compared with earlier
mailings, to news media offices in New York. The Leahy letter was impounded,
along with all other Congressional mail, and was not discovered until Nov.
16. Investigators made painstaking safety and forensic preparations before
opening it in early December.
The analysis of the contents of the Leahy letter is proceeding slowly,
the investigators say, because they are learning the science as they go
along and want to make sure that none of the scarce, lightweight but
extremely valuable evidence is lost, corrupted or misinterpreted. They are
getting help, they say, from scores of scientists across the nation.
"We'll have to take this into court," the law enforcement official said
of the evidence. "We had to assure ourselves that we had a quality
A senior Bush administration official expressed sympathy for the F.B.I.
because the inquiry had grown so scientifically complex and knowledgeable
advisers are so few.
"They're having to review a lot of the initial takes on things," the
official said. "There's an evolving picture. The bureau has gone back to
scratch to invent the science."
But federal experts now say the particles turned out to have a large size
range. While single spores predominated, the experts said, some Daschle
clusters ranged up to 40 microns wide far too big to penetrate human
lungs. A micron is one-millionth of a meter, and a human hair is 75 to 100
microns wide. The big clusters suggested the powder was far less than
Private experts disagree on just how much less. Ken Alibek, a former
Soviet germ official who is now president of Advanced Biosystems, a
consulting company in Manassas, Va., called the Daschle anthrax
"It was not done with a regular industrial process," Dr. Alibek said
an interview. "Maybe it's homemade."
Recipes that antigovernment militia groups circulate at gun shows might
suffice to make the deadly powder, he said.
But William C. Patrick III, a scientist who made germ weapons for the
American military and is now a private consultant on biological defense,
rated the Daschle anthrax as 7 on a scale of 10.
"It's relatively high grade," Mr. Patrick said, "but not weapons
In addition to particle size, federal experts are investigating whether
the anthrax powders have electrostatic charges that affect dispersal and
chemical coatings meant to increase potency and shelf life.
Federal investigators saw the Leahy anthrax as an opportunity to clear
ambiguities and deepen the analysis. Since no powder had been lost in the
letter's opening, they had more to work with. Still, the amount, typical
the tainted letters, was remarkably small just 0.871 grams. A pat
butter weighs 10 grams.
Last week, government officials said the most recent analyses showed
the Daschle and Leahy powders were quite different, the latter finer and
"You can characterize the Leahy as having a smaller particle range,"
In general, he added, the ability of federal investigators to do deeper
analyses because of the relatively large amounts of powder in the Leahy
letter is producing "real interesting results."
A biologist aiding in the investigation said the increasing potency of
anthrax in the letters might suggest that the attacker was a thief who stole
"Maybe he didn't pocket one vial but two or three, if we're assuming
was an opportunist," this scientist said.
Dr. Alibek raised another possible factor. The F.B.I., he said, needed
weigh the possibility that post office sorting machinery might have had
effect. "It could be an additional process of milling," he said, "like a
mortar and pestle."
Experts said the Daschle and Leahy letters, starting at the same place
New Jersey on the same date and ending up at the same destination in
Washington, appear to have taken similar if not identical postal routes.
Alibek agreed but said the same sorter could apply more pressure to one
letter than another. He added that the overall grade contrasts were probably
caused by "different batches of the product, one more sophisticated than
Investigators have also been studying the envelopes, officials say, and
have found that the paper had very large pores up to 50 microns wide.
That is bigger than the largest Daschle anthrax clusters and suggests how
the powder could easily escape individual letters to contaminate the general
"It had to be one of the most porous materials," an official said of
attack envelopes compared with standard ones. "Whether that was by chance
design, I have no idea."
It is sometimes hard even to do reappraisals. In the Florida case, no
letter or residual powder was ever recovered, leaving many questions about
the anthrax there.
Federal officials said the first wave of well-documented attacks with
mailed anthrax in letters from Trenton postmarked Sept. 18 to NBC
News and The New York Post was relatively crude. The powder was
heavily contaminated, they said, with what biologists call vegetative cells
anthrax bacteria before processing in the laboratory turns them into
hardened spores. Vegetative cells in dry anthrax powder are generally dead
and therefore harmless, experts said.
By contrast, the tiny spores live in a dormant state. Individual ones
light enough to float easily in the air and, if inhaled, small enough to
reach deep into human lungs, eventually germinating into bacteria and
causing the respiratory form of the disease, which can be fatal. They can
also cause the less dangerous cutaneous form if rubbed into the skin.
Last October, alarm bells rang when the Daschle powder was found to be
nearly pure spores. The danger was driven home when nasal swabs came back
positive for 28 people in the Senate Hart building, where the letter was
The F.B.I. in early November characterized the Daschle powder as "much
more refined, more potent, and more easily dispersed" than the New York
media anthrax. The mailer's letters hinted at the danger. The media ones
warned the openers to take penicillin. But the Daschle letter said flatly,
"You Die Now."
As federal experts investigated the residual Daschle sample, they found
the picture becoming fuzzier. On one hand, the concentration of the anthrax
was extraordinarily high roughly equal to that made in the abandoned
American germ weapons program, a trillion spores per gram.