Anthrax ping
"Privately, FBI officials doubt that such a link exists."
Leak! Leak! Leak! "Privately" = "Leak"
"They note that the attacks came with an explicit warning --a letter advising the victims to take penicillin, resulting in a far lower death toll"
Just as well could describe it as an ambiguous hint that the later anthrax outbreak would be traced to the letter's message. The first wave didn't work, so a second wave was sent explicitly using the word "anthrax."
" -- but without an explicit claim of responsibility. "It doesn't fit with al-Qaeda's modus operandi," one intelligence official said."
Yes, that makes sense, Osama explicitled claimed responsibility for 9/11. Oh wait, he didn't...well, much later, sort of.