OVM, in the intell business there is almost NEVER conclusive evidence. You have "gut feelings" based on many years of working a problem. You are working with lots of almost unrelated bits of information. In my day we were breaking coded voice communication. A really GOOD code break we were able read 1 out of every 10 words. We employed "fusion" analysis. We would take our 1 or 2 words, match that to a morse transmission that we could not read but it was sent. Then look at a fuzzy picture and some other stuff and piece it together like a puzzle. Armed with that we then would write our "Product" and that, if it was important enough, is what a president would be briefed on.
Then you have to take into account that our agency was not allowed, BY LAW, to share our information with internal law inforcement groups like FBI. Those laws where stiffend up during Clinton making it almost impossible for those who worked the "forgien" problems to pass information to those who worked "internal" problems.
In the aftermath of 9/11 is was very difficult to get good reporting. There was too much finger pointing and blaming going on. Once in a while a report would come out that I could get some "real" information from. They were talking about an "increase in chatter" from the terror net works. That is a sign that something is going to happen soon.
That is what you work with, chatter only. The "Bad Guys" rarely come out and say things like on 9/11 we are going to fly a bunch of airplanes into buildings. What the intell guy would have to look at was more like, "The big game is a few days away, are your pitchers ready?" There would have been a been increase in talk like that.
Then we have to go back to the early Clinton days. When he gutted the intell agencies he got rid of and encouraged getting rid of guys like me. 20 year men, no degree, with pensions. They passed laws limited our ability to get promoted. In the end they bought out as many as they could. Now, it takes 10 years or more for a person to get good at that business. You have to start at the bottom and learn a "target" from the lowest levels of communications and work up to the highest. It you don't learn the small stuff you never understant the big stuff. We lost hundreds of those guys like me and IF we hired new blood on the day Clinton took office and IF they learned the job correctly, when 9/11 happened they were still 2-4 years away from being really good.
Now couple that with the world problems for the 20 years or so prior to 9/11. Most of our meger funds were pushed at the Soviet Problem, out biggest threat at the time. That is what the equipment was designed for. The best and the brightest worked that problem as well, that is where the promotions were. The middle east was an after thought. So there was never the big group of really good agents working that problem and then Clintons move got rid of many of the few good ones there.
That is what really happened. You have to look back 20 to 30 years or more at things like this. 9/11 was just a snapshot in time. The problems go back sometimes more than 100 years and then they bite you. Things like the total underfunding of the intell agencies during my entire 20 years. We never had the ability to even come close to doing the job we were tasked with. There was not enough money.
That is enough for now. I can go into much more detail if you like. It bothers me when I hear things on the news about "failures" etc and read what some "experts" in here throw around as "Fact". The people who work those jobs are good, dedicated people. They were not to blame, congress was. Any failures that took place were 100% caused by politions. Put the blame where it is due. Bush had NOT been in office long enough when 9/11 hit to have had any affect on the agencies. Go back and start looking at the problem since 1950 and then you can begin to figure out what happened. The problems started back then.