There is substantial evidence that thermite was used to cut the central support columns, which caused the towers to fall.
Evidence can be seen on photographs of the columns from the rubble of the World Trade Center.
In this photo, for example, the column directly above the fireman’s helmet shows that it was cut with thermite. There is a substantial amount of hardened molten iron which can be seen on both the inside and outside of the box column. This is precisely what one would expect to find on a column which had been cut with thermite.
Experts who have viewed this photograph say that this column was not cut with a torch.
See our September 11: WTC Controlled Demolition archive
In particular: Physicist says heat substance felled WTC