CHINO (CBS) — The morning after an accidental gun discharge during a police safety presentation at Newman Elementary School in Chino, angry parents want to know — how could this have happened?

Three students were injured by shrapnel after a student pulled the trigger on an assault rifle mounted on a Chino police motorcycle during a school assembly for Red Ribbon Week Wednesday.

The assault rifle, an AR-15, was locked to the side of a motorcycle that was on display. According to Chino police spokeswoman Tamrin Olden, the bullet disintegrated when it hit a metal plate where the barrel rests against the weapons mount. That debris struck three children and caused minor injuries.

Two students were taken to the hospital while the third was checked out on school grounds and released back to parents. The two children who were hospitalized have been released.

A Lodi police officer was shot in the leg in early August when a child pulled the trigger of a gun in the officer’s thigh holster.

The officer was showing off the department’s SWAT truck, vest and other gear at a children’s event called Reading Roundup, when the accident happened.

The officer was taken to the hospital and treated for minor injuries.

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