Police said Friday they arrested 18-year-old Gerald Coats on suspicion of felony assault, child abuse, and trespassing.
Police also arrested a 17-year-old male on suspicion of felony assault.
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Police said Coats is a former student of Dublin Unified School District and may be acquainted with the victim.
Police also said the 17-year-old suspect has a familial relationship with a female student and mother also involved in the incident.
The victim was allegedly assaulted by four suspects and possibly a high school parent on Friday, according to police, who were called to the school about 3:30 p.m. regarding an on-campus fight.
The 15-year-old victim was taken to the hospital with injuries to his face and head.
Police said the boy was allegedly confronted by a high school parent. The boy retreated into the boy's locker room, where he was followed by four suspects and the parent. The suspects, who were wearing hoodies, allegedly assaulted the boy until the fight was broken up. They then fled.
Police said they are still investigating additional suspects, and it appears there were previous conflict between the victim and a female student, who confronted the victim about the conflicts with her mother.
Police said the female student and her mother were not involved in the physical attack and it doesn't appear the mother coordinated the attack.
Anyone who may have information helpful to this case is encouraged to contact Dublin Police Services at (925) 833-6670.