US Spec Ops Command was hyper-sensitive about it's role regarding intra-US operations. They were roundly criticized for their part in Waco and Koresh. We all learned that they are not to take part in any operation within the US, that that is the role of the FBI and the Justice Department.
If these terrorists were in the US legally, then the legal nuances would have been a real headache. I can see them dropping the case and feeling justified for doing so. My guess, though, is that FBI WAS informed. Spec Ops Command has continual contact with the FBI, and what might not have been formally passed along would have certainly been informally passed up the FBI food chain. In fact, I can see them working the subject WITH FBI involvement each step of the way.
I can understand WHY this information wasn't shared...and I have not faulted the actual agents of either department for anything...
What I DO fault is the ones like Gorelick that made it so...and then didn't take any responsibility of heat for it....
UNTIL, hopefully, NOW...