The general theory on this subject is that the explosives were set prior to 9/11. Marvin Bush...George's Brother... was working for the company in charge of WTC security.
Simply use the cover of guards doing their job.... guards working double duty actually black ops specialists who move in and plant explosive charges during the night when nobody's around. They could have virtually full access to entire building with no witnesses.

Charges could be planted on essential structural members in ceiling cavity above ceiling tiles where it is unlikely that anyone would look.

Explosives would not need be wired if remote detonator technology is implemented. The entire system could have been wirelessly controlled using advanced technology. Each floor programmed to a different frequency. Easier than wiring if the budget is there to pay for it.

how many trillion were missing from the Pentagon?

If you research the WTC you will find that for many years the towers did not come close to meeting full occupancy. Other explosives could have been planted by simply renting office space with ficticious company names. Massive amounts of explosives could have been planted in these spaces with an unlimited amount of time to transport them there and set them up properly. These spaces could have also been a hub to move explosives to other areas.

Thermite which once ignited will burn hot enough to cut right thru steel. Was probably used at impact site. the fire would initialize the reaction and when the structure failed and began to fall they simply "Pulled" the building below it from the top to bottom.

Planes for show.... Bombs for Go!