The Real Trolls are the Conspiracy Mongers... It never occurs to them that cutting away walls, insulation, plumbing and electrical conduits in order to place controlled demolition changes on the towers structural columns in advance would not have gone unnoticed. Furthermore, no recorded evidence of explosions prior to the tower collapses by any of the several demolition firms in Manhatten operating sensitive seismographs at other sites in the city exist.
It never occurs to the 9/11 Coincidence Theorists that there is more than one way to destroy a building. With a few trillion dollars missing from the Pentagon on 9/10/2001, you'd think they could invest in wireless technology and exotic explosives (and/or even exotic space-based star wars technology and/or Haitian HAARP) which do not impose the same requirements as "standard" controlled demolitions (CD). If all you are focused on are standard/typical things, all you will see (or not) are what you looked for.
That was the problem with the initial NIST reports on the collapse of the WTC towers: they ruled out CD for superficial reasons, came up with a marginally plausible excuse *only* for the initiation of the collapse based on airplanes, and ignored the rest of the collapse and its glaring anomolies.
FTR, the tenants of an under-occupied structure would not necessarily have to note anything that you point out. New tenants come and go. Renovation work was ongoing. Contractors and vendors are a common site. Few still would notice those on the graveyard shift. Plus, evidence of overnight construction was seen by tenants in the form of rapidly accumulating dust in the offices.
I believe there is recorded evidence of explosions. You better check your facts and provide video links to support your assertions.
The "squibs" are easily explained by floors collapsing emitting debris. A buildup of pressure caused by the compression of air between the floors as they "pancaked" most likely cause the appearance of squibs. Furthermore, videos of the "explosion" show it increasing in intensity with time which is opposite of the way a real explosive detonation works which is to diminish after the initial charge is set off.
Sorry. This explanation is no longer the fable in popular favor even by NIST. You are behind the times and debunk yourself. In plain English, the floors did not "pancake" and the squibs were not caused by compressed air between floors, and you'll find nothing of the sort supported by any (more recent) NIST reports. The squibs, however, can still be explained by CD, as can the pulverization of the concrete, the horizontal ejection of steel and materials at high velocities, etc.
Finally, there was virtually no concrete in the towers which were constructed entirely of steel bolts, trusses and columns none of which could hold up without the support of the others to which they were linked making the collapse of a few columns all that was needed to take down the buildings.
Pulled that one out of your butt, did you?
In the future, please do some research and substantiate your claims with links. In this case, you'll find (even in the pictures of the construction of the towers) that they were composed of substantial amounts of concrete.