Root causes?
"As soon as one kid in a school finds something online of interest "
The fundamental question we need to answer is "why are torture and murder sites interesting to kids?", and then find a fix for that. However the effective answer will probably need such a societal culture shift that it's not going to be deliverable.
Part of that answer is that the adrenalin rush has been exploited for ages to sell goods and services, and unfortunately it's subject to habituation, requiring ever stronger stimuli to trigger it, so the baseline itself has become an excessive level of excitement.
Another part is that passive consumption of electronic media has largely supplanted actually doing things that resulted in sufficient satisfaction at lower levels. When I was a kid, we built and flew model aeroplanes, scrounged components from old kit and built radios, hiked for miles cross country at weekends and played a lot of sport. All of these were challenging and delivered recognition of real achievement, which was our 'high'.
Finally, although it's unpopular to say so, most of us live in societies that are excessively pre-occupied by sex and violence from a very early age (via movies and marketing).
Putting all this together, it's clear that reversing these trends is fundamental to the societal change that might solve the problem. But who among the media moguls and marketeers is going to start?