All the regulations that are meant to prevent “tragedies like these” from happening don’t really work that well. Like most prohibitionist efforts, they are limited by the practical matter of human cleverness. People can and do find ways around most regulations if they really want to. A wall of regulations cannot stop a killer. Only armed people can stop an armed man.
A law enforcement official familiar with the investigation says the three guns found at the shooting site were legally purchased by Nancy Lanza, the mother of the suspect in the shooting.
And no background check would have found anything wrong with Nancy Lanza. The man who might have been flagged by the background check never had to go through it.