I'm glad to hear that your family is a close-knit, loving, supportive one to your asperger grandson. Unfortunately in Adam Lanza's case, it looks like his dad and brother as well as other relatives -- where are his grandparents and uncles, aunts, etc. -- had disappeared from his life entirely. To Adam, it likely felt like complete abandonment. Although Adam's 20 years old, he's still a "child" in many ways as he lacked the ability to function as an independent adult in society.
I think the adult family members should have tried a little harder to include Adam in their lives. Maybe a phone call once in a while to Adam, or even an email or e-card or even a handwritten, snail mail card to let Adam know he's still unconditionally loved? I'm not blaming them for what Adam did, but they clearly were not there for him when he most needed it.
I know mental illness has a way of isolating family members from the mentally ill patient. And that saddens me greatly. I wish there was something done for Adam before he exploded. As hard as it may be for some to feel for Adam, I not only see the 27 who are dead as victims, I also see Adam as a 28th victim but he was a victim to mental illness.