I'm guessing at a plasma device/weapon of some sort. Something special was needed to take out this building, in this fashion, not to mention the core. Was this the cause of the melting cars and trucks? How many people simply "not found"? If this building had collapsed the bodies of the victims would be buried in the rubble, they would not turn to dust. How many "missing"? Vapourised not crushed!

Material sourced here!

http://amanzafar.no-ip.com/WTC/

Updated!

"Plasma-based weaponry is any group of weapons designed to use high-energy ionized gas or "plasma", typically created by superheating, as a projectile. Research in this field of weaponry is in its infancy.

http://en.wikipedia.org/wiki/Plasma-based_weaponry

There has, however, been notable interest in its development. Theorized models of plasma weaponry use high-energy electromagnets to control a burst of plasma and propel it forward, as well as maintain its course over distance (see blooming). Currently these weapons are only in the theorizing stage as there is yet to be a reliable source of high-energy plasma that could supply such weapons. An even greater challenge is to prevent the plasma from expanding, since the internal magnetic forces will cause the plasma to expand and dissolve rapidly, once it has left its magnetic containment field. New breakthroughs in technology such as high-temperature superconductors and nuclear fusion have the potential to allow the development of such weapons.

Most theories, however, have not yet been affirmed. Actual prototypes of such weapons will be dependent upon advances in the fields of nuclear fusion, magnetohydrodynamics, and superconductors. Until then, development of these weapons will be limited to the drawing board."