The kid was mentally disturbed. I don ‘t think a couple of visits with Dad would have made a whit of difference. There are sometimes just bad seeds.
I surmise the problem started before dad stopped seeing him and that is my point. Dad left his son to be raised by a single mother with no masculine influence. A couple visits no, being part of his life, yes.
When you look at pictures of Adam Lanza, you know there was something really wrong with him that was not caused by an absent father or SSRIs or psychiatrists. Even his skull was misshaped. He must have had some kind of inborn problem. People can be born with birth defects in the heart or stomach or kidney, so no doubt they can be born with defects in the brain as well.