From this article:
http://www.seattle911visibilityproject.org/rwtcpdf.pdf
1.1 First experts suggest explosives were used.
On September 11, 2001, American explosives expert Van Romero said: "
My opinion is, based on the videotapes, that after the airplanes hit the World Trade Center there were some explosive devices inside the buildings that caused the towers to collapse.” The Albuquerque Journal further noted: “The detonation of bombs within the towers is consistent with a common terrorist strategy,” Romero said. “One of the things terrorist events are noted for is a diversionary attack and a secondary device,” Romero said. “Attackers detonate an initial, diversionary explosion that attracts emergency personnel to the scene, then detonate a second explosion,” he said. Romero said that if his scenario is correct, the diversionary attack would have been the collision of the planes into the towers. [10]
The next day, Mark Taylor, demolition expert noted in New Scientist: “it cascaded down
like an implosion.” [11]
Webster Tarpley notes European expert sources who immediately
suggested the possibility of explosives in the towers. On Sept. 12, the Danish "bomb expert" Mr. Bent Lund stated: "an estimated amount of circa 1 tons of extra high-explosives bombs
must have been detonated inside the World Trade Center complex in order to make the Towers collapse in the manner they did." [12]
Jens Claus Hansen, a high ranking officer of the Danish Military Academy, on 9/11/01 stated in an interview: “Additional bombs
must have been placed inside the WTC towers--otherwise they would not have collapsed as they actually did.”
Former NATO General Keld Hillingsoe in the same interview stated: “Additional bombs
must have been installed inside buildings.”
On Sept 13, 2001, Hugo Bachmann, Professor Emeritus of building dynamics and earth quake engineering at the Swiss Eidgenossische Technische Hochschule in Zurich saw two
possible scenarios, and
felt that both should be investigated. The first was fire and its effects on the steel supports; the second, an additional terrorist action. The article quoted by Tarpley noted that Bachmann “
could imagine that the perpetrators had installed explosives on key supports in a lower floor before the attack.” [13]
....Although Van Romero later “
changed his mind”, he still admitted the collapses looked like demolitions [16]