Many studies seem to be swaying towards children experiencing childhood trauma as being a contributing factor to violence. It certainly is not going to be unusual for men / fathers to be capable of inflicting trauma and abuse.

Not really isolated incident they all may be fatherless but that then means mother failed even then too small a group to draw conclusions of all fatherless boys how many do this very low number

I've met many kind, decent men in my life whose father's were complete assholes. The paternal presence in the family didn't nurture or protect the children, it damaged them.

Why aren't motherless girls mass murdering?

A more important issue is why all the mass shooters in the US are white. Oh, and have access to AK-47s.

Warren Farrell has written much about boys and was interviewed on BOOK-TV at CSPAN this weekend. He did not speak on this point but his talk started me to thinking on it. Among his credentials is that he was once a National Organization for Women board member.