Looks like those who were questioning the responsibility (or lack thereof) of his mother will wind up being vindicated:

School Shooter’s Babysitter Said The Boy’s Mom Warned Him Never To Turn His Back

The mother of the Sandy Hook Elementary gunman warned the boy’s babysitter never to turn his back on the boy
…
Specifically, Kraft says Nancy Lanza told Kraft “to keep an eye on him at all times … to never turn my back, or even to go to the bathroom or anything like that.”

Even the most charitable explanation for such a warning is that she feared the boy would do something to hurt himself. And yet she kept guns around, and taught him how to use them??