[WS:] According to news report he was diagnosed with Asperger Syndrome which is a part of the autism spectrum. I do not believe that psychopathy is a part of it and based on what has been revealed about him in the media he does not have psychopathy symptoms. AFAIK, this is linked mainly to genetics and neuroanatomical factors rather than upbringing i.e. "fucked up family."
AFAIK, "fucked up family" could be a contributing factor to the behavior in such cases, but not the cause of the disorder. That is different from psychopaths who, as you point out, are are mean and hateful, but also very manipulative so they often appear charming. Lanza's description in the media does not seem to fit this model.
Both appear anti-social but in different ways. Autistic/AS kids appear socially awkward and lacking affect and unable to pick affective clues (i.e. other people's emotional states), so they are often seen as "weirdos" and picked on by their peers. Psychopaths are very manipulative, mean and lacking remorse for their action, but they can act appropriately if they need to. In other words, autistic kids cannot easily hide their social awkwardness, psychopaths can and often do.
-- Wojtek
"An anarchist is a neoliberal without money."