"Based on chemical analysis of WTC structural steel residue, a BrighamYoung University physics professor has identified the material as Thermate. Thermate is the controlled demolition explosive thermite plus sulfur. Sulfur cases the thermite to burn hotter, cutting steel quickly and leaving trails of yellow colored residue."
Portland Independent Media Center
It's a little easier to understand now if Grove's Transcript is to be believed.
They did it for the money.