We not be absolutely certain WHAT caused the fires, but we are certain they were not natural.
They were not started by fire-fighters.
They were not started by an arsonist.
This was much more nefarious in origin.

the answers to some of these questions imo lie in the Dr Judy Wood's info.

It took me 10 years to understand what Dr J is stating.

In short, as I understand the data...

Pons and Fleishman tech for COLD Fusion was stolen in 1989 with the help of 911 'truther' Stephen E Jones.
While Jones Thermate conclusion/narrative is interesting and possible we must recognize the tell tale signs of Thermate being aluminum and iron and sulphur... well excuse me... but the towers were made of Iron and Aluminum clad exterior... not too unusual for iron and aluminum to show up in the remains of an aluminum and iron fire... sulphur... well need I say more?

Dr Judy Woods explains this far better than I can...why how fires occur as they have...after the energy weapon is shut down, that's when fires start. Its called iirc, Hutchison effect.

Dr Wood does a show weekly on AIrStream Radio Character Driven YouTube channel.
She has a book, where did the towers go' and she has a website.

While I might need to write a more extensive article... for now it's best we go straight to DR Judy Wood's website and review her materials.
It took me 10 years to understand what may take others less or more time to grasp.

http://www.drjudywood.com/