There was an anonymous police source on Sunday talking about a rifle in the trunk (not a shotgun). Aside from that, no other stories. Also the first video clearly shows a shotgun taken from the trunk.
A lot of conflicting information out there...
http://abcnews.go.com/Blotter/connecticut-school-shooting-adam-lanza-mother-visited-gun/story?id=17992396#.UNBym3dstYA
Two handguns were also found at the scene, but law enforcement officials described the Bushmaster as the primary weapon.
http://www.cbsnews.com/8301-201_162-57559336/conn-school-shooting-what-we-know/
Police also found a semi-automatic Bushmaster .223 caliber rifle inside the car her drove to the school, his mother’s car, and shell casings inside the school.
The only possible explanation is that the facts are being spun for maximum political gain. The image of little kids being executed with a powerful "assault weapon" is far more useful to the regime than if they were executed with garden-variety handguns. If I sound cynical, I am.