Kathy has merit on this, Kids that do this, are falling into a fantasy world, so by playing the games, getting locked into this world, then taking them to the range. Then letting them watch movies that glorify guns and violence, the copy cat emerges.
Now, not all will fall prey, only a few that the elevator is having issues with getting to the top floor. Shy seems to play a role, a persons ability to get along. This seems to be a key.
Spotting it in school seems to be the place to pick it out. This is where it develops, parents are the other half, they see it. Are they blind to it? Do they say he will grow out of it? Most do. This would be the problem. Ignoring it.