I don't really understand why there would need to have been bombs. You have jets loaded with 20,000 gallons of high octane Jet fuel that impact near the top floor, runs down through the elevator and ventilation shafts into the basement. A building with a cities worth electric and other utilities. Once that fuel flooded the basement, all it needed was to be ignited. 20,000 gallons of Jet fuel would take out a decent sized town I would imagine. In the basement of a sky scraper running all down through the ventilation, elevator shafts, you have the WTC scenario. One big death trap waiting to collapse. That's what it looks to me like happened. Fuel basically ignited, blew it up and it collapsed.
Who was really behind it, what motivation? I can't say but it was definitely a symbolic attack against the Western and our American Financial system. That could be anything from Islam to Communism to Globalism attacking Western Democracy. My best advice is look at who has risen to power since that attack. That would be ALL 3 in my opinion.