In our paper Effective Counterterrorism and the Limited Role of Predictive Data Mining, Jeff Jonas and I pointed out the uselessness of data mining for finding terrorists. The paper was featured in a Senate Judiciary Committee hearing earlier this year, and a data mining disclosure bill discussed in that hearing was recently marked up in that Committee.
On his blog, Jeff has posted some further thinking about 9/11 and searching for terrorists. He attacks a widespread presumption about that task forthrightly:
The whole point of my 9/11 analysis was that the government did not need mounds of data, did not need new technology, and in fact did not need any new laws to unravel this event!
He links to a presentation about finding the 9/11 terrorists and how it could have been done by simply following one lead to another.
Jeff feels strongly that Monday morning quarterbacking is unfair, and I agree with him. Nobody in our national security infrastructure knew the full scope of what would happen on 9/11, and so they aren't blameworthy. Yet we should not shrink from the point that diligent seeking after the 9/11 terrorists, using traditional methods and the legal authorities existing at the time, would have found them.