Well this was debated the other day! Looks like someone had to come clean!
http://politichicks.tv/2013/01/nbc-admitted-no-assault-rifle-used-in-newton-shooting/
The video you reference in your post was the report Pete Williams did on 12/15, the day after the shooting. It is being used as though the report came out today. It did not.
This has been hashed, rehashed, and then refried like beans.
That’s nonsense early reporting when things were confused long repudiated. That’s Alex Jones/Infowars level stuff.
https://www.youtube.com/watch?v=dSO1nOnLe9E
Things that make you go "whoah"...