defending, hasan said the taliban. >> anyone who knows the facts know that this was a terrorist attack. >> reporter: the obama administration has refused to call it that. 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