Adam Peter Lanza, perpetrated the Sandy Hook Massacre. He was addicted to violent video games, which incited his ruthless murdering of 20 young schoolchildren and his own mother. Adam Lanza did not actually have a criminal record, nor any infraction with law enforcement.
He was a student at the school for a short time, but was then transferred to St. Rose of Lima Catholic School, and then Newtown High School, where he was an honours student in English and Mathematics. His mother reportedly considered homeschooling him, but decided to send him to public school instead.
Allegations that Adam Lanza suffered from a mental illness are unsubstantiated.
Students and teachers who knew him in high school described Lanza as "intelligent, but nervous and fidgety". He avoided attracting attention and was uncomfortable socializing, and was not believed to have had any close friends while at school.  His brother, told law enforcement that Adam was believed to have a personality disorder and was "somewhat autistic". An anonymous law enforcement official, who was friends with his mother, Nancy Lanza, stated that he had been diagnosed with Aspergers, previously.
Knowledge of firearms
Close friends of his mother, have testified that Nancy Lanza was an adamant gun enthusiast, possessing several guns. . She often took her two sons to a local shooting range, taught them, in particular Adam, how to shoot, in the hope that it would teach him some responsibility. Also, he was a prolific contributor to mass murder articles at Wikipedia. 
- Adam Lanza: Wikipedia author, The Daily Caller, July 2, 2013