of course it could be kept a secret, while at the same time allowing for people to take part without their knowledge...

remember the feds were running drills on 9/11 of planes hitting buildings...just a coincidence, which is why when you hear some ATC recordings from that day, you can hear them asking if it's "real world or exercise" when they find out there are hijacked planes...

so you create confusion with drills as a cover for the real event...same deal with the 7/7 london bus bombs...

but all one has to do is do a little research, and the 19 freedom hating muslim hijackers commanded by the guy in the cave on the dialysis machine conspiracy theory falls apart...it doesn't explain even close to anything that happened on that day...

unless you believe a short, superficial explanation...they hijacked the planes because they hate our freedom.