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A 12-year-old boy fired a gun he found in an unattended bag during dismissal at a Bridgeport elementary school, shattering a school bus window, according to Chicago police.

A man left the gun on the bus outside of Minnie Miñoso Academy, police officials said. The boy found the bag and fired a single shot at around 2:25 p.m. Monday.

Police said the man took the gun and fled. No injuries were reported and area detectives are investigating.

In a letter to families, Miñoso Principal Carrie Cole wrote that the school “will continue striving to provide all students with a safe learning environment.” The gun was never on Chicago Public Schools grounds, she said.

“Thankfully, no one was injured, and all students are safe,” Cole wrote.