Well ... the folks here (excepting shills) don't need convincing re: 9-11 (Let it happen or made it happen) it was an OP.
NOTE: noone222 said from the beginning that demo explosives may have been built into the Towers as part of the original construction but the authorities wouldn't want the general public to be aware of it. (Nor would many others such as Insurance Companies and especially people required to work in them).
Another thing to consider is how easy it would be, if they do build these demo explosives into all / most skyscrapers, to set em off all across America in a coordinated effort to create chaos. [It will be difficult to determine the origins of the devices. There may even be a national alert stating that some other country has launched nukes (think about Obama's new internet/mass media control system for emergency announcements).
I have predicted a nationwide-multi-city attack since the day they passed NAFTA because there is no other legitimate reason to export all of America's jobs while inviting unemployed foreigners into America by the tens of millions OR MORE.
The next thing to consider would be who did it (we know who is ultimately responsible) and where they're hiding. Napolitano has announced an increased terror threat ... and I believe her. The only difference is that I believe in a different perp, the U.S. FEDERAL RESERVE BANK GOVERNMENT. The FED is run by Jews. Jewish lightening is the historical method they use to eliminate evidence of their frauds. (Too many people are awakening to the truth and they have no doubt about that fact).
Personally, I believe every major city in America is a potential target with some metros having a higher potential than others depending upon the strategic advantage or disadvantage they afford the elites.
People smarter than me should be able to think of many additional factoids that support the notion presented in this post. As for me, I've already seen enough !