but officials are pushing back at critics who accuse them of labelling it nothing more than an office shooting. the army sent a letter to congress saying there has been no decision to classify this shooting as workplace violence. before the attack hasan exchanged 20 emails with a cleric. the evidence indicates this was the alleged criminal act of a single individual. >> just to say he's a terrorist doesn't really explain what he is. terrorism is a tactic. he used the tactic of terrorism. >> reporter: this professor is a former military lawyer and terrorism expert. he says hasan's new admission clearly shows that he's identifying himself as an enemy combatant in league with the taliban. >> what caused him to do it. he's a radical islamist extremist self-identified with the taliban.