The towers were not felled by conventional means and Danny can see no signs of the controlled demolition process he is an expert at.
The thing is, the buildings didn't collapse either, they turned to dust.
How is this guy supposed to consider the use of nuclear devices?!
It's outside his field.
He says: "No conventional controlled demolition of the towers.
CCDs use the weight of the building to break it, without that you'd need masses of explosive, or some other form of energy input.
Like a nuclear bomb.
