The problem with the investigation is that the FBI's culture is one that is derived from investigating standard domestic criminal actsIt is a law enforecement mantra - certainly the view overwhelmingly promoted by the FBI - that there is no such thing as "terrorism" until someone takes credit for the act.
I've seen several LEO-types (including retired FBI managers/agents) pronounce this "unerring truth" on the news, with an unmistakable tinge of arrogance and condecension.
Yet that no one ever took credit for the first WTC bombing, the Cole, 9/11, the Yemen oil tanker, or Bali seems not to disturb their whacky "definition" of terrorism one iota.
It's quite clear why the FBI has been incapable of thwarting terrorism on U.S. soil. By their definition, there isn't any! (OK, maybe the Weathermen in 1968)
The FBI is completely out of touch with reality, and unforuntely they are able to cram their whacky views down the throats of local law enforcement.
"It is a law enforecement mantra - certainly the view overwhelmingly promoted by the FBI - that there is no such thing as "terrorism" until someone takes credit for the act."
I certainly agree that this seems to be a part of the current dogma of the FBI. However, I don't think that in this instance they really believe it. It is merely a convenient fiction behind which they can take shelter.
The FBI like any Federal agency takes its cues from the administration in power. No administration wants to admit they are relatively powerless to protect its citizens from acts of terrorism. It is political suicide. As others in this forum have already alluded to such a revelation would be guaranteed to create additional panic. A situation that would probably be further exploited by the terorists and certainly by one's political opponents. Ergo if another plausible explanation can be found we almost never have acts of terrorism commited within the confines of the United States.
Unless and until the present administration is prepared to accept the inherent political risks of admitting that these shootings are in fact acts of foreign based terrorism we can only expect the FBI and other Federal law enforcement agencies will be very reluctant in getting too far out of line with the White House's posture.