In other words, no, there was no credible, independent investigation at the WTC site.
That's what I figured.
You figured wrong, reasoning, as you do, from a position of absolute ignorance of procedures.
I don't know whether I can dumb this down enough that you can, with your limited understanding of fire investigations, grasp the basic principles of forensics that come into play in this sort of situation.
Investigators ask questions aimed at figuring out
Who did
What,
When,
Where,
How and
Why. Usually, there are not several million eyewitnesses to any given crime. In this case, there were.
We know the time of the strikes of the two towers and on the Puzzle Palace and the crash at Shanksville. We know that it involved flying stolen airplanes into the targets that were hit and into the ground in the middle of Pennsylvania.
We know the times that the airliners were hijacked. We know the airports from which the planes were hijacked.
Right out of the box, we had the When, What and Where.
How they got control of the aircraft could not be determined from anything that they could find at the target sites. That would have to be determined from communications with people elsewhere, surveilance tapes at the airports. The black boxes were only important to coroborate those findings. The chances that they would find the black boxes in a recognizeable condition the GZ were slim at best. Nothing in the world is utterly indestructible. Black boxes are tough, but not so tough that they would survive the collpases of the towers.
Who did it would not be found in anything at GZ. Why they did it would have to be figured out from what evidence they could find at the airports.
So, investigators knew that the buildings collapsed because a group of criminals drove airplanes into them and set them on fire and the fires weakened the steel until it did what steel generally does when kept hot enough long enough.
It bends and drops its load.
No fire fighter with an IQ north of 100 doubts that. There was no sign that anything else had happened.
NIST and FEMA were only interested in how the buildings fell because it was their responsibility to figure out whether anything could be done to make it less likely that this sort of thing would happen again if somebody went kamikaze with an airliner or there was a major fire that could not be fought.
They did not have to look at the steel where it was to figure that out, and the rubble couldl not be left where it was for them to inspect because there was a fire under it that had to be put out as soon as possible. The investigators from NISTand FEMA were of no use on the pile. The cops, fire fighters and iron workers all had some training to tell them whether something looked wrong as they pulled it from the pile. They could tell the nerds at Fresh Kills that they needed to look at such unusual things.
So, yes, a proper investigation, to the extent that it could be done there,
was done at GZ. If dirtbags like Alex Jones, Dylan Avery, Chris Bollyn or Eric Huffschmid tell you it wasn't, screw them. They lie a lot. Especially that piece of crap Bollyn. He's a Nazi. Lying is what he does for a living.