Not too sure of what is associated with autism, but several years ago I had a 10 year old child “attack” me while doing work at a customer’s house for no obvious reason. He was just doing something in the other room and suddenly ran past his father and started growling and pounding his fists on me. Parents were apologetic and told me that he had autism. They must have known he had issues because one of them was always between me him.
I have reviewed the literature on Autism/Asperger's and violence. There are no studies which indicate that a person with Autism/Asperger's is prone to engage in planned violence, especially not of the nature involved in this shooting. Autistic individuals may at times engage in spontaneous acts of violence, as what you reported with the child of your customer. Adam Lanza's behavior was planned behavior, and is not that seen in persons with Autism.
However, there is a large number of cases of individuals with either schizophrenia or some form of a personality disorder who have engaged in planned violence that mirror what happened in this case. The Arizona shooting, the Mall shooting in Washington State, the Colorado movie theater shooting, and the Columbine High School Shooting all fit that mold.