Your option 2 doesn't appear to me to be a tenable position. Even if only a few people in the U.S. knew it, there would also be Iraqis and al-Qaeda terrorists who would know it. Leaks could come from anywhere. There would also be the scientists (Iraqi?) who would have carried out the weaponization; even if they didn't have direct evidence about the letters, they would know about the weaponization program.
It's not just the sheer number of people who would have to keep quiet, it's the variety of loyalties they'd have. Somebody would have revealed something.
Options 1 and 3 are almost as unlikely. All that's left is 4 or (from a different post) 5.
Considering that the Bush administration doesn't have a stated position on the source of the anthrax, it probably doesn't isn't meaningful to ask where the administration thought it was from, as if the people in the Bush administration had to have a uniform opinion. I presume that some people in the administration thought Iraq the likely culprit, some thought al-Qaeda, and some thought neither.
So you rule out al Qaeda entirely?
Lately, the idea that the anthrax mailer was an opportunist acting in the wake of 9/11 seems exceptionally unlikely to me. The motives and the circumstances don't add up. What motives, after all, have been suggested? The main suggestions I've seen are: (i) it was a warning about the bioterror threat, by someone who had no foreknowledge of 9/11; (ii) it was an attempt to frame Iraq, by someone who knew 9/11 was coming. (Partisans of 'none of the above' are herewith invited to post their ideas about motive.)
For (i), we have to imagine someone sitting on a stash of weaponized anthrax, so worried about the bioterror threat that they're thinking of faking an incident. Then boom, out of the blue 9/11 happens; and a week later, they think, "Gee, I'd better mail out those letters, just in case we get complacent about terrorism!"
Suggestion (ii) - who would want to frame Iraq? People mention Iran, Israel, and the Bush administration. But if Iran was behind the anthrax, it makes much more sense to suppose that they were behind 9/11 as well, which would make this a position-3 theory. (I'll come back to this possibility...) As for the other two, well, I'll debate those possibilities if anyone cares to defend them, but in brief I think it would be a strategically illogical way to proceed, and also supposes powerful yet sociopathic cabals of a sort that I think simply doesn't exist in those societies.
I have more time for the idea that it was al Qaeda acting alone, or that someone other than Iraq was the state sponsor. The former option apparently requires that the potency of the anthrax has been overstated, a path I won't explore here. In the latter case, let's specifically consider Iran for a moment. You might suppose that Iran has been working through al Qaeda all these years, trying to make it look like Iraq by carrying out attacks on days of Iraqi significance. The aim might be to get the USA to support a Shiite uprising, which Iran could later control; but Bush outwitted Tehran by invading Iraq with a massive American force, rather than attempting regime change on the cheap, as was advocated by the Iraq hawks circa 1999.
Where this theory initially founders, in my opinion, is on the Kuwaiti connection. Abdul Basit Karim (aka Ramzi Yousef) grew up in Kuwait, was there when Iraq invaded, was described as a collaborator by the Kuwaiti interior minister, and his itinerary beyond Kuwait was added to his file by Iraqi intelligence during the occupation, suggesting a cooperative relationship. He does not seem a very likely candidate for a plot meant to injure Iraq.
There are some other "what ifs" that I haven't mentioned, e.g. what if al Qaeda got the anthrax from North Korea, what if they got it from freelance Biopreparat scientists, etc. I guess we'll get around to those in due course!
I presume that some people in the administration thought Iraq the likely culprit, some thought al-Qaeda, and some thought neither.
In Woodward's NSC scene, they consider Iraq and Russia. I've also been told that Iran, Iraq, and Saudi Arabia are the three candidates for state sponsor of al Qaeda which are seriously considered in Washington.
The Bush administration may not have a stated position - but the FBI does. According to the FBI they believe the source of the anthrax was domestic. When you think about it, they must be very confident that this is true. Imagine the consequences for the FBI if there had been massive follow-up attacks and that Al-Qaeda took reponsibility. It would, on the face of it, have been unthinkable of the FBI to have made such an error early on - lulling the country into a false sense of security that an Al-Qaeda type group did not possess anthrax.
So what really led the FBI to make such a bold assertion in the first place? Was it the handwriting analysis? Doubtful.
It must have been something else. Perhaps the weaponization signature really does have a US lab written all over it. But if that's true, why are they still sniffing around Detrick? Detrick haven't handled any dry powders for decades. The only two labs that may have manufactured dry powders in recent years are Dugway and Battelle. If these labs ever shipped any samples to Detrick they were always converted into wet slurries.
Even if Dugway or Battelle had made live anthrax spores with silica and polymerized glass - how on earth could such a weapon walk out of these places?
None of this makes much sense. The anthrax mystery will likely continue for many years. However, unlike other mysteries like the Kennedy assassination or TWA 500, the anthrax mystery does have solid evidence that could solve it. That is, the forensic analysis of the spore coatings.
So why has that forensic analysis never been released? The usual excuse is that this is an ongoing investigation, but when will this excuse no longer be a valid one? After 3 years? 5 years? 10 years?
Some people, including the attorneys for Maureen Stevens, are attempting to use the power of the courts to force the FBI to reveal the nature of the evidence. The FBI have fiercely resisted - citing an ongoing investigation. For how much longer will they get away with this?