There's a reason the second tower hit was the first to fall. Steel can become pliable when subjected to heat. Say the kind of heat generated from an explosion and fire cursed by an accelerant. The second plane hit lower in the building. The weight on the structure was greater because there were more stories above the impact area that the fatigued steel was forced to support.
And for the "controlled explosion" theorists out there I have two questions: 1) What was the building supposed to do except fall basically straight down and, 2) if you were at the site in the weeks after it happened you'd see many buildings surrounding it with chunks torn out of their fascade due to debris not falling directly down.
You have to ignore so much to buy into any of these theories that I find it alarming that anyone could believe them.