Many firefighters and others reported explosions below the impact and fire floors. For example:

• Genelle Guzman, the last survivor to be rescued from the WTC 1 rubble, reports that when she got down to the 13th floor some 20 minutes before the North Tower collapsed, she heard a “big explosion” and “[t]he wall I was facing just opened up, and it threw me on the other side.”
• Firefighter Edward Cachi said: “As my officer and I were looking at the South Tower, it just gave. It actually gave at a lower floor, not the floor where the plane hit. … [I]t went in succession, boom, boom, boom, boom, and then the tower came down.” [6]
• Firefighter Kenneth Rogers said: “[T]here was an explosion in the South Tower [WTC 2]. … Floor after floor after floor. One floor under another after another and when it hit about the fifth floor, I figured it was a bomb, because it looked like a synchronized deliberate kind of thing.” [7]
• Stephen Evans, a New York-based correspondent for the BBC, said: “I was at the base of the second tower … that was hit. … There was an explosion. … The base of the building shook. … [T]hen there was a series of explosions.” [8]
• Firefighter Louie Cacchioli reported that upon entering the WTC’s lobby, he saw elevator doors completely blown out. “I remember thinking,” he said, “how could this be happening so quickly if a plane hit way above?” When he reached the 24^th floor, he encountered heavy dust and smoke, which he found puzzling in light of the fact that the plane had struck the building over 50 stories higher. [9]

There were also reports of explosions in the basements themselves. For example:

• Janitor William Rodriguez reported that he and 14 others in the North Tower heard and felt an explosion below the first sub-level office before the aircraft impact, he said, the floor beneath his feet vibrated and “everything started shaking.” Seconds later, so he added, “I hear another explosion from way above. … Although I was unaware at the time, this was the airplane hitting the tower.” In any case, he said, co-worker Felipe David, who had been in front of a nearby freight elevator, came into the office with severe burns on his face and arms yelling, “explosion! explosion! explosion!” [10]
• Rodriguez’s account was corroborated by José Sanchez, who was in the workshop on the fourth sub-level. Sanchez said that he and a co-worker heard a big blast that “sounded like a bomb,” after which “a huge ball of fire went through the freight elevator.” [11]
• Engineer Mike Pecoraro, who was working in the North Tower’s sixth sub-basement, said that after an explosion he and a co-worker went up to the C level, where there was a small machine shop. “There was nothing there but rubble,” said Pecoraro. “We’re talking about a 50 ton hydraulic press – gone!” They then went to the parking garage, but found that it was also gone. Then on the B level, they found that a steel-and-concrete fire door, which weighed about 300 pounds, was wrinkled up “like a piece of aluminum foil.” [12]

Moreover, if there were explosions in the basements of the towers before they came down, we would expect them to have caused the ground to shake. And several people did, in fact, report shaking.

• Medical technician Lonnie Penn said that just before the collapse of the South Tower, “I felt the ground shake, I turned around and ran for my life. I made it as far as the Financial Center when the collapse happened.” [13]
• Fire patrolman Paul Curran said that he was standing near the North Tower when, “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.” [14]
• Lieutenant Bradley Mann of the Fire Department saw both buildings come down. “Shortly before the first tower came down,” he said, “I remember feeling the ground shaking. I heard a terrible noise, and then debris just started flying everywhere. People started running.” After they returned to the area, so he said, “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.” [15]

In addition to the testimonial evidence about explosions in the towers, there was physical evidence provided by the nature of the collapses, which involved features generally only consistent with intentional collapses brought about via controlled demolition. For example:

• Sudden Onset: In controlled demolition, the onset of the collapse is sudden: One moment, the building is perfectly motionless; the next moment, it suddenly starts coming down. But when steel is heated, it does not suddenly buckle or break, but bends and sags. So if heat could induce a collapse, the onset would be gradual. But as videos show, the buildings were perfectly motionless up to the moment they began their collapse. [16]
• Straight Down: The most important thing in a controlled demolition of a tall building, which is close to other buildings, is that it comes straight down. Mark Loizeaux has said that careful planning is needed in setting the charges “to bring [a building] down as we want, so … no other structure is harmed.” [17] If the 110-story Twin Towers had fallen over, rather than coming straight down, they would have caused an enormous amount of damage to buildings covering many city blocks; but they did not. [18]
• Rapid constant acceleration: Measurements show that when the North Tower collapsed, it accelerated constantly at approximately two-thirds the rate of gravity. [19] Such acceleration is incompatible with the official explanation of the building collapse. The official explanation of the collapse of each of the Towers claims that the top part of the building, above where the planes struck, came down on the structure below and initiated total collapse. If that were what happened, the lower stories would have provided significant resistance and a deceleration of the top section would have been observed, had there been an impact. As videos show, and as careful measurements of the motion of the top section confirm, the upper stories of the building fell down through the lower stories with a high rate of constant acceleration and no associated deceleration or impact. This means that the official explanation is false. [20]
  It is clear that most of the columns of the lower stories must have been destroyed by some force other than gravity, such as explosive force, so that when the upper stories came down they encountered little resistance.
  This analysis has been validated by measurements of the Verinage Technique of building demolitions, which actually uses the momentum and kinetic energy of a falling upper section to break up the lower section without the use of explosives. In those cases, deceleration of the top section is clearly observed. [21]
  A further analysis showing that the columns of the North Tower could not have been involved in resisting the collapse has recently been published. [22]
• Total Collapse: These 110-story buildings collapsed into piles of rubble only a few stories high, even though the buildings contained a remarkable 283 columns supporting each story, with 236 closely spaced large steel box columns as part of a robust Vierendeel truss network on the exterior, and in the core of each tower 47 steel box columns, the bases of which were massive. [23]
• Pulverization and Dust Clouds: “At the World Trade Center sites,” said Colonel John O’Dowd of the U.S. Army Corps of Engineers, “it seemed like everything [except the steel] was pulverized.” [24] Although this was an exaggeration, much of the non-metallic contents of the buildings was indeed pulverized into tiny particles of dust, giving rise to enormous dust clouds, which impeded visibility for a half hour after each collapse – even though, according to the official theory, the only physical agencies involved, after the impact of the airplanes, were gravitational acceleration and fire. [25]

In disputing the view that the destruction of the towers was the result of controlled demolition, NIST said: “Video evidence … showed unambiguously that the collapse progressed from the top to the bottom.” [26]

The implicit argument being made by NIST was based on two presuppositions: 1. Controlled demolition must begin from the bottom. 2. The collapses of the Twin Towers began at the top.

However, both of these presuppositions are false.

1. As the first statement by Mark Loizeaux quoted above indicates, controlled demolition usually begins from the bottom. However, physicist Steven Jones has pointed out, the top-down destruction of the towers “is unusual for controlled demolition, but clearly possible, depending on the order in which explosives are detonated.” [27] Conversely, a natural gravitational top down collapse replicating the observed phenomena is impossible.
2. Although the collapses appeared, to people watching them on TV, to have begun with the impacts and resulting fires, they for the most part began, as testimonies above indicated, with explosions in the basements. Interestingly, they also initiated just above the impact damage.

Seismic waves provide one more type of evidence that the buildings were brought down by explosives that were below ground at the beginning. That issue is explored in Point TT-7: “Why Did the Twin Towers Collapse? The Seismic Evidence.”