Logistically and strategically, it would have been simpler to obtain a surplus airliner, move it to a remote location near the target. Refurbish it, load it with explosives, then fly it at the target. They would have the advantage of time and would not have to penetrate airport and airline security. Such an operation would also show that airport security is immaterial to protecting the public.
But then what do I know.
Taking it a step further...why even use a jetliner?
If somebody wanted to deliver a nuke or even a lot of explosives, wouldn’t an ordinary run of the mill private airplane do the trick? They could just steal one from the local air strip hangar and skip the whole hijacking a jetliner step.