I am not one for conspiracy theories, as regular New Statesman readers know. But this week I must air an intriguing possibility: why have there been no arrests or charges in the anthrax investigations, following the five deaths and mass panic more than ten months ago? "The longer nothing happens, the more one is forced to come to the conclusion that there is a reason why the process is not going forward", Dr Barbara Hatch Rosenberg - chair of the Federation of American Scientists' working group on biological weapons and an academic at the State University of New York - tells me.
In other words, is a cover-up going on? The FBI says it has interviewed 5,000 people, issued 1,700 grand jury subpoenas, polygraphed hundreds of people and created 112 databases in a continuing investigation that has so far cost many millions; it says that it has reduced the number of suspects to a net of 30. But in the tiny world of biological warfare experts here, one name is on everyone's lips. I shall call him "Dr X", though I know his real name and whereabouts.
The FBI has searched his home twice, polygraphed him and interviewed him four times; it has now privately told his new employers at the National Center for Biomedical Research and Training that he is no longer a suspect. But the circumstantial evidence against the 48-year-old man is startling.
From 1997 to 1999, he worked at the US Army Medical Research Institute of Infectious Diseases at Fort Detrick, Maryland - the American equivalent of Porton Down - an hour north of DC, where (according to his own 1999 CV) he acquired a "working knowledge" of "wet and dry BW [biological warfare] agents and knowledge of how to produce Bacillus globigii", a chemical offshoot of the lethal anthrax. He was among a small number vaccinated against anthrax.
It is now beyond doubt that the lethal doses of anthrax, as I revealed here last 10 December, were from the Ames strain and obtained from US military sources (that is to say, Fort Detrick).
It now seems likely that the anthrax was sent by an American who had no wish to kill people, but merely to hammer away at his hobby-horse: that the US is unprepared for a biological warfare attack. Dr X, after leaving Fort Detrick and working for the Science Applications International Corporation, even commissioned a study that included a scenario of an envelope containing anthrax powder being released in an office. Following his exclusion from a terrorism seminar in 1997, Dr X wrote to the organisers protesting his absence; "I am tremendously interested in becoming more involved in this BW [biological warfare] area," he wrote.
But Dr X's earlier background is even more intriguing. He was brought up in Illinois but obtained medical and other doctoral degrees in what was then Rhodesia, and South Africa. In his CV, he claims he worked with the Selous Scouts (the Rhodesian equivalent of the SAS) and had contacts with South African intelligence, too.
This leads us to a compelling question. In his period there (1978-80), why was there the biggest outbreak of anthrax in modern history - among Rhodesian blacks (affecting 10,000) as they fought for independence? Eerily, Dr X worked close to the Greendale part of Salisbury (now Harare): and the name of the fictitious school in New Jersey that was the return address for the anthrax letters of last September? "Greendale" school, fourth grade.
Then there are the hoax letters. It is not generally known that a series of hoax letters - supposedly containing anthrax but in fact with harmless powder inside - started as early as 1997. One was sent to B'nai B'rith, the best-known Jewish group in the US, with a letter saying it contained "anthracks" (the real ones last September had similar unconvincing misspellings such as "penacilin"); this, presumably, was a crude attempt to suggest that illiterate Arab terrorists were the culprits.
Dr X later would exhort his colleagues to "Remember B'nai B'rith!"
In February 1999, there was another round of anthrax hoaxes, all using the same type of block capitals used in the deadly letters: and all contained about the same amount of powder as the real ones, roughly a teaspoonful.
A letter was sent in 1999 to a post office in Georgia next to the Fort Benning military base, with a letter urging in large capital letters: "WARNING: THIS BUILDING AND EVERYTHING IN IT HAS BEEN EXPOSED TO ANTHRAX. CALL 911 NOW AND SECURE THE BUILDING. OTHERWISE THE GERM WILL SPREAD." The deadly attacks of last September conveyed similarly dire warnings.
But nobody took any serious notice then, and it took last September's wave of deaths and panic - in my view the anthrax threat created more panic, certainly on the east coast, than the 11 September atrocities themselves - for the anthrax attacks to be taken seriously. Following them was a wave of hoaxes, most of which were clearly that: but a handful, because of their style and manner, were taken seriously and may have been linked to the September killer. One included a letter to Senator Tom Daschle last November - one of the original recipients who was sent enough real powder in September to wipe out everybody in Washington and beyond - postmarked London. I'm told that Dr X, who travels widely, was in Britain at the time.
Why the US military took Dr X - with his self-professed history of aiding racist regimes in southern Africa - on to its payroll at $58,000 a year at its 650-strong research facility at Fort Detrick is anyone's guess. He worked there with the Ebola and Marburg viruses, not anthrax: but he had access to the (then) rather loosely organised labs that were dealing with anthrax, and was once caught with a girlfriend in a so-called "hot zone".
When he left Fort Detrick in 1999 to work in the more lucrative private sector, he was given a "Secret" security clearance - but, for reasons I do not know, that was abruptly withdrawn last August. When friends visited him at a service flat he used last year, he gave them all Cipro to take - the antibiotic used to ward off anthrax.
So where does all this place us? We have a man who was obsessive about the dangers posed by biological warfare attacks; who was one of a minuscule number who had the access and knowledge to produce the kind of finely milled, weaponised anthrax spores that killed five, made many more ill, created mass hysteria and put tens of thousands of people on antibiotics; whose repeated warnings about attacks, specifically anthrax, had been humiliatingly ignored; and who, finally, is likely to have become further embittered by the removal of his security clearance last August. Are there not too many coincidences suggesting that Dr X may have been the culprit?
But this is where the conspiracy theory runs deep. I offer no opinion on it, only the facts.
Were Dr X to be publicly charged, might he have very damaging information to impart about US assistance to the Rhodesian and South African regimes? About the shambolic conditions at Fort Detrick while he was working there? About offensive biological warfare programmes there, even though the military insists it does defence research only? Might he not be a veritable landmine of dangerous, damaging and embarrassing information?
Though she will not actually say so, Dr Rosenberg clearly believes there has been a cover-up: she describes the FBI's investigation of Dr X as a "sham" but is no more certain than I am that he is the guilty man. What she does say is: "The likely outcome for the investigation is continued stalemate." Meanwhile, the significance of the anthrax attacks last September cannot be overstated. "By breaking the taboo on the use of bioweapons, this event has engendered a future threat that could dwarf 9/11," she says.
And not even the mighty FBI, it seems - "seems" being the operative word - is able to get to the bottom of such a mystery.