Florida is also heavily populated but the density is nowhere near that of New Jersey, nor are there numerous Saudi Arabians in the Palm Beach area.
That some aspect of this event would incidentally include New Jersey is not unlikely. That any aspect would include Boca Raton is exceedingly unlikely as an incidental matter.
I can go down the street about 1/4 mile and stop into any one of 5 halal butcher shops. They have give-away newsletters concerning the various Islamic communities in the US. Some of these newsletters come from New Jersey. Some are from Detroit. Others are locally generated. A terrorist would have ample resources to use to concoct fake return addresses in New Jersey.
So far not a single person who has been detained in New Jersey has been demonstrated to have any real relationship to the anthrax attack. There were people detained. There were thorough searches of homes and businesses. Cars were examined in great detail. The lifestyles and relationships of hundreds of people were looked at with a fine-toothed comb. Mailboxes were ripped out of the ground and studied.
On the other hand we now have a confirmation that at least one of the Florida based attackers was diagnosed as having an anthrax-like infection, and he was treated. Two others in Florida sought medications for what could be cutaneous anthrax. One of the victims in Florida was married to a woman who was known to two of the attackers.
The evidence points to Florida, and to people in Florida who had relationships with some people in New Jersey, Virginia and South Carolina. The logical conclusion is the anthrax attack was mounted from Florida by terrorists residing in Florida. An accurate understanding of normal postal operations illuminates the process.
New Jersey's not just an incidental coincidence of a place in this.