Rigging the building- there was a large amount of short term, sudden work done on the interiors of the buildings in the weeks before 9/11. This was done at night, some claims about "asbestos checking" or other reasons were given. Multiple reports form workers in the buildings about this happening, with large work crews in there. (I am relating the reports I have heard, and thus what I believe people believe- the answers to the question- I'm not stating this happened as an objective fact, I cannot prove it. I am not taking a position on its veracity or most of the explanations I give below. I'm merely relating the beliefs of other people.)
It of course seems mighty coincidental that there was this asbestos remediation work and inspections going on in these buildings right before the attack. There are a lot of such coincidences, such as the unusual insurance situation with the twin towers right before, the head of security of the twin towers being related to the administration, the fact that there was a "scenario" being "war-gamed" on that very day (allegedly) that involved jetliners hitting towers-- and then it actually happens?! To be honest that just seems like sloppy work.
Also, in a controlled demolition situation there is a characteristic sound of the many charges going off. This sound has been reported by many witnesses on 9/11. Of course they are all just people- office workers and the like, but even some firemen- so they aren't "authorities". But multiple explosions before the collapse are a common eye witness claim.
Slow acting thermite vs shaped charges- I don't know what the common theory is, but I've seen arguments that shaped charges were used, particularly based on the cuttings in some of the beams in wreckage that was exposed. I'm under the impression that most who believe the controlled demolition theory believe that it was shaped charges. I'm not sure how or why thermite would be involved.
How to keep the conspiracy theory under wraps? That's the easiest part.
Ever watch the show "Penn & Teller: Fool Us"? Particularly if you binge watch the show it's kinda amazing how every trick fools you and you have to take a few minutes figuring it out. Sometimes you can figure it out easily, sometimes you're stumped. But the ones that stump you, if you go online and find out how they are done are obvious in retrospect.
The unfortunate reality is that we are not as objective as we would like to believe. What we believe is in large part based on what we want to believe. We want to believe our eyes so when the girl magically appears behind the sheet on stage we want to believe it is magic, and most people just go never knowing how it is done. On some level they know, but they don't look deeper.
Misdirection is very powerful. People are not in the habit of looking for it, and its easy to knock down online as "paranoia" when it is pointed out.
Further we are raised from kindergarten to believe in the government, that the government is benevolent and that we can trust our rulers. It's hard to overcome that and be objective. You know in North Korea they feel the same way. In Japan during WWII many people sacrificed themselves because they loved their Emperor. People worship dictators, its' easy to believe they will give more than the benefit of the doubt to a democratically (in theory, 2000 is another bit event) elected president.
The very week of 9/11 people were talking about how those buildings wouldn't fall naturally like that, and what we've had since then is 15 years of an Official Conspiracy Theory (the al queda box cutter theory) propagandized far and wide and any alternate theories, or even people asking questions shot down as "conspiracy theory's" or elsewhere here in this thread "truth bullshit".
Personally I don't know what happened. I don't believe things went down as they are claimed exactly- I'm incredulous that the entire air force stood down for a day when just a year earlier they were on a rogue lear jet in 15 minutes after loosing contact with it.
But the most telling thing is the term "Al Queda". Al Queda was, we were told in the late 1990s "the CIAs code name for the mujahideen fighters they supported in the afghani war in the late 1980s". But somewhere after 911 "Al Queda" became not a code name to describe a group of unorganized people, but a sinister organization with "cells" everywhere.
This means that Bin Laden somehow-- and here I'm imagining Tom Cruise getting the NOC list in the first Mission Impossible, only with a robe and a long assed beard hitting the floor-- snuck into the CIA and found this top secret code name "al queda" and then decided to name his massive organization by that name?
You're right, you can't keep this massive conspiracy under wraps. You can't make a woman appear out of thin air.
It doesn't matter.
Most people won't believe it.
Germans for years couldn't accept that the Holocaust had happened, and right under their noses. After all they arent[ monsters.
Many still don't want to believe it.
I don't know what happened, but it's not like the Official Conspiracy Theory is an open and shut case.