Newtown killer had used the guns registered to his mother.
And mommy tonight him to shoot
IIRC Lanza did try buying a gun himself, but had a panic attack and couldn't complete the transaction. But I don't think he was registered as a prohibited individual with NICS.
I think Lanza should have been included -- and mom would have then needed to make a "straw purchase" of firearms for him. She's dead, of course, but the fact that she was committing a felony with a possible sentence of ten years in jail and a fine of up to $250,000 might have given her pause.