How do you know if Nancy Lanza had a gun safe or not ?
Maybe Adam broke into her gun safe or figured out the combination over time or find the keys to her gun safe or whatever ?
She took him shooting with her, and trained him at a time when a reasonable person quite likely ought to have known that he was mentally unstable. If she kept her guns locked up, obviously the degree of security employed was insufficient. She didn’t deserve to die for that lapse in judgment, but neither did a host of innocent children. We’ll certainly find out more in the near future.