Neither video in the link you provided worked...Got another link? One that works? Perhaps from the ACTUAL source and not some third-party<quoted text>NBC Admitted: No 'Assault Rifle' Used in Newtown Shooting
Or, maybe we need only take note of the "Editor's note" at the bottom of the page to debunk your claim:
"Editorís note: Connecticut State Police have confirmed that Adam Lanza did, in fact, use a Bushmaster .223 high capacity rifle and two hand guns. As far as we can tell, NBC has not issued a retraction."
Just scroll to the bottom of the page and read the notation directly above the Faceboof and Tumblr links.