Adam Lanza apparently also had a personality disorder. People with autism are generally non-violent to others on a large scale like this. Those with a personality disorder on the other hand, suffer symptoms such as:

Frequent mood swings
Stormy relationships
Social isolation
Angry outbursts
Suspicion and mistrust of others
Difficulty making friends
A need for instant gratification
Poor impulse control
Alcohol or substance abuse

courtesy of: [link to www.mayoclinic.com]

Where you will also see that personality disorders range from paranoid to schizotypal to anitsocial personality disorder (aka sociopath). Long story short...the kid was MESSED UP BIG TIME!!! Likely nothing to do with his autism!