The September 11th attacks actually working without terrorists going rogue, getting caught, missing their targets, or screwing up borders on ASB to begin with. So, the fact that it worked against humongous odds, would seem to me not to need tinkering with. Any tinker screws it all up due to butterflies. The idea that blowing up some gas trucks (because those are so easy to buy, I bought one on Tuesday) or randomly shooting children (which would be confused as either inner city violence or, if it were intentionally done in suburban schools, it would remove any claim to moral authority which in reality Al Qaeda was making--why not just light kittens on fire and threaten to do so every 30 minutes until your demands are met? Talk about not being taken seriously.) Being that we know that three out of four the planes hit, if the two DC planes' men were dedicated to follow up car bombings weeks apart after 9-11, maybe they can get the US to have a permament feeling of fear. But, in reality, we had anthrax in the mail weeks later and then a plane crashed in the middle of Queens NY in November...so we already had that feeling anyway. Pretty much, 9-11 was Osama's sickle cut. Screw with it and you screw everything else up.