Three children suffered minor injuries after their 9-year-old classmate brought a BB gun onto campus and fired it on the school playground on Thursday morning, Nov. 14 officials said.

Police said the boy brought the air gun to Washington Elementary STEM Magnet and shot three classmates between ages 9 and 12 on the playground.

The three were struck, but not seriously hurt.

The boy was detained and then released to the custody of his mother. His name was not public because of his age.

The child’s motive was unclear.

The Pasadena Unified School District said it has launched an investigation into the incident and is cooperating with police.

The school is “implementing an enhanced awareness of safety by both students and staff, and encourage everyone that if they see something to say something to an adult on campus immediately” and counselors are also available to students, a statement from the School District said.

“The student will be subject to appropriate discipline,” the statement noted.

The incident occurred the day after officials said a 16-year-old student  killed two of his classmates and injured three others.