“Would NSA surveillance have stopped 9/11 plot?”
Effective Counterterrorism and the Limited Role of Predictive Data Mining
by Jeff Jonas and Jim Harper
http://www.cato.org/pub_display.php?pub_id=6784
While this 2006 paper primarily focused on highlighting the limited role of predictive data mining towards counter-terrorism — this paper also presents evidence that 9/11 could have been averted without the currently contested meta-data collection program OR even new technology, for that matter.
I was working with watch lists, private and publically available data immediately after 9/11 in attempts to assist our nation … as such many of the insights presented in the “Hiding in Plain Sight” section are largely based upon my first hand experience.
That said … in my opinion, while “more data (e.g., population-wide meta data collection) could be helpful in uncovering criminal activity” — this was not essential to detect and possibly preempt 9/11.  And even if such data was provably helpful, is it really constitutional?  Hence the vibrant debate …
Jeff Jonas