Given that such prep not only takes a long time but is very visible, and the fact that those buildings were all heavily used and had foot traffic around the clock, here are the questions you need to address:
1. If all three buildings were indeed wired with explosives, when were they so wired without anyone noticing anything at all?
2. How did the demolition teams manage to get in and out without arousing so much as a peep of suspicion, with absolutely no one coming forward after the event to say that they saw or heard suspicious activity with people tearing up floors and drilling holes in walls? That is, after all, what demolition teams do. No security guards, no cleaning teams, no late-night workers, no one at all said they heard or saw anything at all.
3. If the buildings were supposed to appear to collapse naturally, why would the explosives teams take all that time and so precisely place the explosives so as to make the collapse appear unnatural and risk drawing attention from conspiracy theorists? It would make more sense to be sloppy.
4. We know that secrets held by more than one person inevitably surface. Why has absolutely no one come forward in over 20 years even hinting that he/she was involved in secret drilling, tapping, and setting explosives to kill American citizens? Not even crackpots, and crackpots will falsely confess to murder. No deathbed confessions, nothing.
It's all fine and dandy to insist there were explosives, but they don't materialize from nothing with no one noticing anything.