A 15-year-old boy who attended a middle school in Kawagoe, Saitama Prefecture, has been in a coma since January after he was punched and kicked by three of his classmates, according to investigative sources.

The then second-year student had reportedly been a target of chronic bullying by the trio since enrolling in the middle school in 2010. The municipal school had acknowledged frequent troubles between the boy and the trio, but failed to recognize them as bullying before the incident, according to the sources.

The incident occurred on Jan. 5 during a winter recess. After finishing morning activities related to a sports club that the boy and the trio belonged to, the three told the boy to come with them to a city park where they allegedly punched and kicked him repeatedly. Noticing that the boy had stopped moving, one of the three called for an ambulance.

Prefectural authorities arrested the three later that day on suspicion of injurious assault. They were later sent to a juvenile reformatory.

The trio reportedly told the police they punched the boy because they "disliked the boy's attitude," claiming the beating was the result of a "one-on-one fight" rather than bullying by the group. Further investigation, however, led to the suspicion that the three likely assaulted the boy in turn while surrounding him.