I doubt we'll ever get to the "bottom", OR the "top" of this.
They're very well protected. I call them the White Mob.
Drugs are very profitable and tax free, especially when you control the supply lines and use corrupt military channels, which in turn are protected and covered up by the CIA, FBI and NSA.

I started my interest with this about 20 years ago at the tail end of Iran Contra. I knew some political writers who quickly got me up to speed on the cast of characters. I got to follow the trials and the money laundering and you have your usual cast of characters.
They're still with us today. They were often convicted, but received cushy sentences, and then were promptly exonnerated by Reagan or Bush Sr. A lot of them hold official positions in today's administrations. You tell me, what's changed?

>you suggest that the hijackers were serving as drug-runners for someone big.

They would have to be "big" because all the policing agencies ignore the offenders and change the laws for them. They have a "get out of jail free" card, it seems. I know a lot of pilots. Trust me, if the FAA wants to get you for a seatbelt harness or irregular flight schedule, you're grounded. Mohammed Atta didn't even register his flights. Some were taken on planes that weren't even licencsed to fly. Things were fudged. The owner of the flight school, Rudi Dekkers, was in business with Wally Hilliard, whose jets have been caught ferrying heroin and fying Saudi nationals out of Florida. Did I mention Hilliard is a big campaign contributor to Jeb Bush? I've seen photos of them together. Katherine Harris was pushing Hilliards Air Line.

>when you get to the top, what do you find?

People who are afraid to talk. People who admit that things are changed, covered up, but that they have families, and they back down. This is from a lot of the aviation officials in Venice, Florida, right on up to the local FAA, sheriff's department and court house.

>Are we talking about an administration complicit with the terrorists in order to "justify" their war?

I've thought of this myself, and I think the answer is no.
Someone was making loads of money from this. I could say I know someone who knows someone who knows what Jeb Bush was doing back in the late 70s and early 80's here in Florida, but hey, I've got a family. Florida is a pretty small place with lots of coastline and small airports. I used to live in Key West. This whole state is tangled up in the drug trade. Over the years I've met lots of people who have worked both sides. It's very interesting. I have lots of stories to share, but certainly not on-line.

>Did they have prior knowledge of the attacks, and permit them to occur so they could scare the freedom out of Americans?

Doubtful. But the guys at the "top" HAD to know there were rogue "mules" delivering the stuff. Sometimes, you just want the money in the bank; you don't care how it gets there, or what filth it running it. It was a gamble, and it back-fired, as it eventually should have.

>Sometimes, the suggestion seems to be that the supposed hijackers were in fact just scapegoats, and the planes were flown by others. Can we reasonably speculate about who those others might have been?

I think this is an erroneous assumption, but I could be wrong. Order the book. Read who's involved. I passed on an extra copy to a fellow or two in military intelligence through a go-between. They were floored. Even THEY had no idea the shenanigans that were going on.
Eventually, someone's gonna slip up and there will be hearings. But the perpetraitors always walk. They have the money, the power and enough of the bad guys to clean up their mess.

We really are at a disadvantage. That it's immoral, illegal, and that many innocent people die along the way, is of no consequence to them..

See if you can find this old book published in 1991 "Called to Serve" by America's most decorated Green Beret Commander, James "Bo" Gritz.
You'll get the background on Richard Armitage and his drug lines through South East Asia during the Vietnam war. The group in power got their start back then.