"So how do we get the guns away from the maniacs then?"
Proper state and federal mandated criminal checks along with mental health checks may be a good start. Not just giving Joe Public a three day cooling off period. How can it be that a person can go along to a gun fair and buy weaponry without any form of check. This is what the Columbine two did.
America is a violent country.
Many "stable" people have guns in their possession and as another poster has rightly pointed out such a weapon is more likely to be used against another family member accidently or deliberately. How many US homeowners have ever had training in either gun usage or safety or same or had thoughts re safe storage of such weaponry?. Surely a person would not think it a good idea to keep a loaded weapon on a nightstand but this does happen.
"Gun laws won't help since most of these guys get them illegaly anyway".
Following Columbine security became the main issue; not gun control laws. This is why such controls were weakened.
What if it turns out that this person held all this weaponry perfectly legally?. Which is Virginia with lax controls is probably likely.