Arch-conspiracy theories like that by LX-GB1 and others are not helpful and show a complete lack of undertsanding and credibility of the poster. Please stop speculating if you don't understand aircraft and ATC architecture.
Suggesting that the 9/11 aircraft were remotely piloted singles posters out for their own stupidity. Suggesting that a standard FBW aircraft could be remotely hacked and flown is equally stupid. Comparison to a specially equipped 707 and 727, just on principle that they were made by the same company as this missing aircraft surely has to qualify for some sort of cretins' award?