I think the basis for the conspiracist's is that it's possible to create an endpoint wavelength which is different from the sum transmitted matrix of wavelengths that creates it.
I guess in a metaphysical term (using sea waves) it would be like two or more waves in the sea colliding together to cause a peak that is not naturally occurring without this number of waves. Obviously sea waves and RF waves are different, but hopefully you get the gist.
As for is it possible?
Well I wouldn't know about the WTC, but I would know that currently no countries is openly identifying RF misuse or applying TEMPEST shielding against misuse (other than in regards to Military Operations that have the shielded tents to stop eavesdropping)
If (from the perspective of others) it was possible to manipulate people through RF, everyone is at risk be they a bum on the street or a Politician acting as a countries Premier. (i.e. President, Prime Minister) Obviously the higher they are up in hierarchy the worse it is since they could make crucial decisions about country operations, observe military operations as well as make economic decisions that could be manipulated by a third-party to whatever endpoint.
(One of the many reasons why I can see flaws in a Representative Republican or Dictator system)