A person his age may very well have had access throughout his childhood to all the world's ugliness.
Maybe; But so did most (or at least many) people his age.
If your hypothesis, that "access throughout ... childhood to all the world's ugliness" causes people to become assassins, is correct, then how do you explain the fact that assassination remains such a rarity? Where is the spike in such assassinations, tracking the spike in Internet access in the last thirty years or so, that your hypothesis predicts?
My point is that he lived a childhood very very different from mine or even my 33 year old daughter's.
My point is that so did everyone else his age, but they are not all out there assassinating people.
More speculation than a "hypothesis". Speculation from reading the Reuters article about him; his opportunities, college if he wanted and if the reports of his testing scores are accurate, he likely would have breezed through, then voctech school and a seemingly responsible home life.
But then what happened?
I wonder about the influences on people his age and younger as we are just coming in to a generation immersed in not just everything on the internet but social media, if I use the rise of facebook as a benchmark. This is wholly a part of their social development and goes far beyond anything previous generations may have had to deal with.
No "they are not all out assassinating people" as they do not all think with one mind. But based of reports on how social media affects the mental health of children, I don't think minors should have access to social media at all. I see no disadvantage to their having to interact with peers the old fashion way. I can only think of a handful of people who would be disadvantaged.
I'm just not inclined to wait for a body of evidence. The mental health reports are enough.
At least now we have mental health apps. A solution to a problem that need not exist.