You seem rather ill-informed about what Tiahrt does. It prevents the BATFE from sharing data about gun traces with anyone accept law enforcement involved in a bonafide criminal investigation or prosecution. Without going into too much detail, this more or less will tell just one thing: where and when the gun was originally legally purchased (or any other FFL that owned it). As there is no question as to where Hasan obtained his weapon, I fail to see of what relevance Tiahrt is to this particular case. As the BATFE had likely never run a trace on a new gun, there would be no data for them to share with anyone.

By the way, I would be willing to bet that drivers license records have been misused far more than anything protected by Tiahrt. And, I would win that bet.