My understanding is that this killer fumbled in the operation of the rifle and that is what brought him down. I dont think AR-15s are any more useful in these shootings than a lot of other weapons, maybe less so than some. The main reason they use them is that they know it will get them more attention since the media and pols go nuts when they find out it was an AR-15.
I agree. A lunatic armed with a Remington 870 with short deer barrel and bag of buckshot and deer slugs would probably be more deadly in these shootings than the guy with AR-15.