shhhhh... it was nano thermate.
an "explosive" so powerful you only need a few grams to bring down any building no matter how large...
but you have to hit the tiny bomb with a jumbo jet to make it go off....
the truth is (as apposed to the Troof), Thermate is just Thermite with powdered sulphur mixed in. as a result it "burns" about 20% hotter, but it is much more prone to self-ignition, and it sometimes just fizzles if the mix is not uniform (such as when it settles after sitting for YEARS in the janitor's closet on the 88th floor...)
and niether Thermite, nor the much less commonly used Thermate come in any variety which can be described as "nano" since they are merely a gross mixture of powdered iron oxide (rust) powdered aliminium, and a little bit of powdered magnesium as a starter (plus some sulphur powder for Thermate), and they are ignited by ordinary fire, but are dispersed if you crash a jet into them since they are fine friable powders.
the cllaims of finding "Thermite/Thermate residue" (which is little balls of melted iron and steel from the reaction) are based on the entirely expected result of the building's contents (which consisted of ample iron aluminium sulphur and magnesium) in the conflagration which resulted from the impact of 2 jumbo jets and their kerosine fuel...
also, the buildings contained NUMEROUS electrical transformers on various floors (as all high rises do), and anyone who has ever seen it happen knows that when exposed to fire (or lightning, or a car crash) an electrical transformer explodes violently.
but yeah it was all a plot by the US government, the jews, and i assume, the 7 foot tall lizard people from the 8th dimension who's dimension runs on the power of children's screams (and they are also jews...)
see david icke's collected works for more information on the 8th dimension aliens and their Monsters Inc. style power source...