This is the latest I'm hearing from gun fetishists. Somehow this is a big media conspiracy and the ar-15 was in the trunk the whole time.
According to Wikipedia, the ar-15 was used inside, a shotgun was in the trunk.
Far as I've heard, the ranges involved don't really make much of a difference between either weapon, it was all practically point blank. The only bonus for a rifle with a large magazine is more shots before roloading.
I just find this argument infuriating about as much as birther and truther nonsense. The only googling I could find on it not being an ar-15 goes to the usual nut sites and stormfront.