It's certainly possible and even believable that it could have been an inside operation. Given the massive expansion of govt. powers as "one" of it's effects here, it's not unbelievable that it could have been engineered specifically for that purpose as part of a larger plan.

Then again, what if it were a corporate operation undertaken by a security consortium poised to reap the benefits from the outpouring of security devices required post 9/11? That's realy no more far fetched than the other idea, is it?

The possibilities are pretty endless in what could have happened or even what other failed operations might have been a part of it all. With all the variables it's hard to be definitive in saying one knows anything for sure except that on that day several orchestrated tragedies occurred at a great cost in lives, money and personal freedom (<-and this cost has yet to even have been completely tabulated as we loose more every year since!)