Hi man,Well, I presume the answer will be "the CIA".
Whoever it is has to have access to missiles and missile crews, demolitions teams with tons of thermite, either has to have access to holograph machines of very advanced nature or has to be working closely with someone who can recruit suicidal hijackers. I guess that would be MK Ultra so more CIA. And mostly, they need to have access to the "flashy thing" from 'Men in Black' that erases the memories of the thousands of people who were involved with or knew something about the highly complex multipronged operation. That sounds like Area 51 people. So Military Industrial Complex + CIA + space aliens/lizard people?
Well Hurm and Star Monkey, who done it?
Am not going to pretend to have done a deep dive on 911.
If they they are going to bring the CIA into though i think they have to be a bit more specific than 'the CIA'.
Is like answering the question 'who were the hijackers?' answer 'Arabs'
Maybe they could start with a list of the names of the hijackers and we see how we go