Quite some time ago, there was a kid that shot a bunch of kids in a school, “one shot one kill - acquire a new target”.
The kid played a lot of first person shooter games, which actually train you in this very thing.
Any wacko nutjob could have access to FPS games.
I have long considered that a major factor in these atrocities might grow out of the envy that youth, who have been brainwashed by Leftist influences into not accepting values that traditionally have motivated decent & constructive behavior, have against those who still display a more purposeful existence.
Can I prove it? Maybe not. But the theory appears to fit a lot of these situations.