It depends upon how the shooter was communicating. If face to face then eye or ear witnesses will be needed. If using a phone, then a warrant issued to the phone company will probably be sufficient. No NSA needed.If multiple shooters – this is really a question to the US citizens here: I’m sure it would be easy for the officials to identify the deceased shooter. Could they afterwards use the NSA to find out who he’s been communicating with to find out who the other shooters were? Would this classify as a terrorist attack and warrant NSA involvement?
Until the shooter motive is revealed, we won't know if this is a terrorist attack.
Ranb