If you have ever purchased a first day of issue envelope, it could be postmarked for anywhere in the US, but odds are it was physically present in the salt mines at Kansas City (where they do the cancellation).
What we have here is a small mailing of a handful of envelopes simply tossed into some collection boxes in Florida on a Friday evening or Saturday afternoon (when there is very little mail entered).
USPS puts large trays called "flat trays" in the bottoms of collection boxes. The collections driver pulls them out and places them in the back of his truck as he taps the boxes for mail.
If Mr. Atta dropped the envelopes in several different boxes, we have a situation where a couple of envelopes are in a large tray. The tray is stacked on top of another tray, and another tray is placed inside it - and on and on until we get a stack of trays.
These trays look like they are EMPTY.
Since empty equipment tends to pile up in South Florida, it gets shipped back North. It's stacked up on a pallet and then shrinkwrapped to hold it together for shipment. Mostly empty MTE, or empty mail transport equipment is shipped North to Washington BMC, Philadelphia BMC and the Bulk and Foreign facility in New York Metro.
From there it is sent to large mailers or post offices needing MTE.
As the empty trays are pulled off the stack to be used for new mail to be sent to the post office, any stray Single Piece Rate First Class Mail will be found by the employees (postal or private) and sent over to the dispatch area. The mail will then travel to the post office in a tray thereby bypassing the collection boxes or letter drops at the main office or in stations and branches.
The pieces postmarked in New Jersey DID NOT CONTAMINATE any collection boxes, letter drops or mailboxes anywhere in New Jersey. That means the letters arrived at the Hamilton Twp. facility in a letter tray ready for cancellation at 010.
This also means that the letters probably were in a stack of trays sent to a large private mailer in the area. Since the letters actually were postmarked, that means the mailer happened not to have handled them on his equipment. This is a sign they were identified as "nixies" or "slugs" by his employees. This information was not passed on to the post office which is why the letters were sent through the cancellation machines. This forced some of the anthrax out through the "wings" in the envelopes and led to serious contamination.
The letter carrier there got her anthrax directly from one of the flat trays. They are used by carriers to carry or tote mail from their work stations to their vehicles for delivery. It was just a case of bad luck.
There are fewer mysteries in this than you can believe. The FBI ran after myths and rumors. They should have asked USPS mail processing system analysts what might have happened and then counseled their investigation accordingly. Instead the FBI investigators believed they knew how the USPS works, and unfortunately counseled their investigation with a layman's knowledge.
While the FBI was digging up mailboxes in New Jersey, they did nothing to pursue evidence in Florida.
Others posting here recall my story has been consistent since day one. All evidence uncovered since the attack on AMI was first reported tends to support my thesis.