Have you read the article "I am Adam Lanza's Mother"? She tells the story of her defiant son?

I have read the article you are referencing. It is actually titled "Thinking the Unthinkable". It was the media who re-titled it "I am Adam Lanza's mother" (which is a line in the blog).

I know that at least some of the other boys she mentions in the article did have father's present in their lives. She stated in the article that SHE is a single mother, but she was not trying to insinuate that all of those mothers were as well. It simply says "and their mothers" because she thinks from the perspective of a single mother, and possibly because mothers are usually the primary caregivers of their children, even if the fathers are present.

Anything is possible but the fact is that you don't know, I don't know, nobody knows. Sometimes the mothers are horrible human beings and deny the father any contact with the child. So don't assume that an absentee father is absentee by choice.

Anything is possible. But I don't think it's the reason why they become mass murderers. there are plenty of murderers who are from nuclear families.