Your homework for tonight:
/1/ His conventional intelligence agents smuggle sealed crates into the USA; suitcases, boxes, whatever. These agents are unaware of the contents, it's just another delivery job. They follow orders blindly because they are constantly tested: get it wrong, your children will be tortured to death back in Iraq. This is the type of things agents do routinely; bring in radio transmitters, guns, cash, explosives, false documents etc. Standard everyday stuff. The agents put the sealed boxes into caches. They can be buried, put in mini storages, safe houses, whatever. Standard stuff, not rocket science. The agents just preposition the stuff, they don't know what it is, it's just another job and they go home to Iraq.
/2/ When Saddam wants to "fire" his prepositioned WMD, he merely contacts Al Queda and tells them where the crates are hidden. They are jihadis out to kill infidels right away, they do not wait for further instructions, if you tell them where a box full of one kilo jars of anthrax is hidden, they will begin to use them right away. They are the "second key" in Saddam's dual key fail-safe system.
Targets can be the subways of ten major cities, and our entire USPS, UPS and FedEx system. Forget whether there are 1,000 or 100,000 casualties, our economy will be utterly wrecked by a 100 kilo anthrax attack. We still have major postal centers shut 16 months after a 3 gram warning attack.
And I believe the modality of that attack may prove my thesis: when Saddam wanted to send a "warning shot" across our bow, he only had to have his Iraqi intelligence agent pass 3 grams of anthrax (less than a film can full) to Atta in Prague.