The reason they are careful about announcing stuff is that in the first hours after an attack they have a short Tim to collect intelligence and get to rolling the group up.
We should be used to this by now. Yet I still read posts by people who think they have a “right” to know everything right away. Unless you have a relative in that bar, your “right to know” is trumped by the need to close down this cell.
NBC refused to tell what the FBI had already announced, that he was an American citizen and not from the Orlando area and had leanings to Islamic extremism. If the FBI knows he is am American citizen, then they know considerably more about him.
I would assume they are trying to circle his accomplices.