Police have arrested a teen suspected of involvement in a knife attack Tuesday on a 9-year-old boy — causing serious head trauma — who was returning home from school in Shizuoka Prefecture, local authorities said Wednesday.

The suspect, who claims to be 18 years old, was arrested for trespassing on school property. Police are investigating the attack as a case of attempted murder.

Firefighters received an emergency call from a woman at around 3:50 p.m. Tuesday saying she had found the boy lying in the road. They found him about 300 meters from Takasu Minami Elementary School in the city of Fujieda.