How they imploded the WTC, page 1

Here's how the twin towers fell, they both collapsed from the top and their top sections crushed the rest of them below:

And here is how they did it:

How Building Implosions Work

The basic idea of explosive demolition is quite simple: If you remove the support structure of a building at a certain point, the section of the building above that point will fall down on the part of the building below that point. If this upper section is heavy enough, it will collide with the lower part with sufficient force to cause significant damage. The explosives are just the trigger for the demolition. It's gravity that brings the building down.

Of course they had to blow the basements before the collapse to help weaken the entire structures and what better time to do that then right when the planes crashed into them:

William Rodriguez, a 9-11 Survivor
Arriving at 8:30 on the morning of 9-11 he went to the maintenance office located on the first sublevel, one of six sub-basements beneath ground level. There were a total of fourteen people in the office at this time. As he was talking with others, there was a very loud massive explosion which seemed to emanate from between sub-basement B2 and B3.
Just seconds later there was another explosion way above which made the building oscillate momentarily. This, he was later told, was a plane hitting the 90th floor... He heard explosions both before and after the plane hit the tower.
A fellow worker Felipe David came into the office... "He was burned so badly from the basement explosion that flesh was hanging from his face and both arms." William asks: "How could a jetliner hit 90 floors above and burn a man's arms and face to a crisp in the basement below within seconds of impact?"

Photo showing white smoke emitting near the base of the WTC 2.

At about 6:45 he went to the mechanical shop in the second subbasement...
Deep below the tower, Mike Pecoraro was suddenly interrupted in his grinding task by a shake on his shoulder from his co-worker.
His co-worker made the call and reported back to Mike that he was told that the Assistant Chief did not know what happened but that the whole building seemed to shake and there was a loud explosion.
By this time, however, the room they were working in began to fill with a white smoke.
When the two arrived at the C level, they found the machine shop gone.
The two made their way to the parking garage, but found that it, too, was gone. He was convinced a bomb had gone off in the building.

Then after they blew the basements, they blew all the explosives up, down, and around the buildings:

Fire Captain Karin Deshore
Somewhere around the middle of the World Trade Center there was this orange and red flash coming out. Initially it was just one flash. Then this flash just kept popping all the way around the building and that building had started to explode. The popping sound, and with each popping sound it was initially an orange and then red flash came out of the building and then it would just go all around the building on both sides as far as could see.
These popping sounds and the explosions were getting bigger, going both up and down and then all around the building.

Links to witnesses of the WTC explosions:
revereradionetwork.com...
killtown.911review.org...