This comment from bmaz is also rather insightful.
The problem is, sometimes dots are just that – dots unconnected, and reasonably so. I am not sure that if everything had been known and added together that Hasan merited that much more attention than he was apparently given. What would have been done? Arrested? For what? A surveillance team placed on him 24/7? Unlikely. Discharge from the service? Based on what? With the exception of the gun purchase, which was legal, all his activity was at least marginally consistent with his position, duties and religious beliefs.