The investigation was unable to find a motive other than to conclude that the killer was obsessed with mass murders and had “significant mental health issues.”
Nancy and Adam Lanza were said to have been close, with the mother not afraid of her son, but allegedly afraid for him.
Earlier this month, US authorities released recordings of emergency calls made by trapped and terrified people from within the school as the killer stalked the classrooms.
Lanza drove to Sandy Hook Elementary having that morning fatally shot his mother in the head as she lay in bed.
On arrival, he killed the school principal and a psychologist in a hallway, then shot dead two adults each in two first-grade classrooms, and shot 15 children dead in one classroom and five dead in the other.