There's a Franklin Avenue in Princeton. It runs parallel to Nassau Street.
I believe there was another mailbox in DC that also tested positive.
Don't forget, the old swab tests are considered garbage.
If I were going to put Anthrax in the mail and wanted to make sure it got there, I'd put in a the box near the post office just before pick up time and watch it get "into the system".
In investigating, I'd look for a pattern..e.g. Tuesday seems to be a favorite day...Who has off on Tuesday??? and can run around doing errands???
Everything was happening on Tuesdays...
Sac