So, I was wondering what kind of gun that the Sandy Hook shooter used, so I googled it. It's a Bushmaster AR 15. Why anyone who isnt in a paramilitary squad needs a gun like this, I dont know, but it's what he had. Anyway, this image is from the Cabela's ad that I used to see the gun.
I dont know how well you can see it on this copy, but here's a clearer image of the yellow box at the bottom.