http://www.dailymail.co.uk/news/article-2248782/High-school-tech-club-student-turned-cold-blooded-executioner-How-classmates-remember-genius-Adam-Lanza.html

Here is an article that discusses this shooter.

I think that some of the characteristics of Asperger's can contribute to incidents like this - difficulties connecting with others and having social contact, and deficits in understanding and expressing emotions. I don't think that a lack of empathy is really the right characterization - we struggle with theory of mind, and don't pick up on how other people are thinking or understand our own emotions or how to talk about them. People can't tell how distressed we might be, because we don't know how to tell them or show them. There is also sometimes a distorted sense of justice - overemphasizing the pain that someone else caused to us in comparison with ideas of retaliation, justice, or making them feel the pain of what they did to us.

That said, I don't think that people with Asperger's are more likely to become violent than anyone else is. I think that I am extremely peaceful (even if I did joke about blowing up teachers' cars in high school when I felt hurt by them), and I think that most of us are really very peaceful.