This obviously suggests powerful explosives were used to destroy the structural supports of the towers just prior to their collapse.
Source: The New York Times
Testimony of medical technician Lonnie Penn (see page 5 of PDF file for below quote):
"We felt the ground shake. You could see the towers sway and then it just came down and I never looked back once I started running."
Testimony of fire patrolman Paul Curran (see page 11 of PDF for below quote):
"...all of a sudden the ground just started shaking. It felt like a train was running under my feet. . . . The next thing we know, we look up and the tower is collapsing."
Testimony of Lieutenant Bradley Mann of the fire department (see pp. 5-7 of PDF file for below quotes):
"Shortly before the first tower came down I remember feeling the ground shaking. I heard a terrible noise, and then debris just started flying everywhere. People started running...."
"...we basically had the same thing: The ground shook again, and we heard another terrible noise and the next thing we knew the second tower was coming down."
Huge ground shake before collapse
Uploaded by chipmuck. - Technology reviews and science news videos.
Notice how the stationary camera shakes from the ground shaking @20-22 seconds in the above video of the North Tower collapse. The North Tower collapses approximately 12 seconds after the ground shaking (begins at 33 seconds in video).
- WhatReallyHappened.com: "The Ground Shake Preceding
the Collapse of WTC 2"
- WhatReallyHappened.com: "Eyewitness Reports Of Explosions Before WTC Collapses"
- WhatReallyHappened.com: "Video Evidence of an Explosion at the Base of WTC 1"
- Images of the World Trade Center Site Show Thermal Hot Spots on September 16 and 23, 2001 (U. S. Geological Survey Report)
- WhatReallyHappened.com: "Thermal Hot Spots: Fingerprint of a WTC Demolition"