It’s actually pretty simple. Lanza brought a Bushmaster AR-15 rifle and two handguns—a Glock 10 mm and a Sig Sauer 9 mm—into the school with him. He used the AR-15 to shoot everyone else, and one of the handguns to kill himself. The shotgun was left in the trunk of his car, which is the gun seen being taken out of the trunk in the overhead video.
The problem with that is the feds told the media it was an AR 15 in the trunk, not a shot gun.
If the feds don't know the difference, then we really are screwed.