The age of knowledge

There is an age within Christianity one becomes responsible for their sins. I don’t remember what that was called or exactly how old one had to be. I began thinking of this, when the motive began to emerge for those horrible killings in the Amish school house in Lancaster County, Pennsylvania. The news is reporting that the gunman had been greatly upset and troubled by his molestation of the two relatives when he was twelve. They said he said he was having nightmares and having those feelings again. I wondered if those relatives were much younger or were close to his age. I also wondered was he truly a predator or indulging in sexual experimentation. Evidently that event was powerful and made more so by an immature mind. Apparently there was no one to confide in, no one to help or even to notice. Has a mind left in ignorance has created this catastrophe?