UTSUNOMIYA, Japan - A series of viral videos showing students assaulting their peers has triggered police investigations, school interventions and a surge of online abuse, highlighting the growing risks of violence amplified by social media.

In January, a widely shared video showed a male student at a prefectural high school in Tochigi Prefecture, north of Tokyo, punching another student. The footage, which quickly circulated online, led prosecutors in Utsunomiya to refer the student to family court on suspicion of causing bodily injury.

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