Surveillance video from inside a Baskin Robbins in East San Jose shows a man and child walking in back on April 26.
Video shows a man running up, smashing the window as shards of glass rain down on the child.
The man then leans in and shouts something.
The incident was never reported, so the child remains unidentified.
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Police did not learn about it until receiving a tip on May 2.
Officers arrested the suspect last week
"We know they weren't known to each other, so we can't speak to the state of the mind of the suspect or what may have let him to do that. We just know it was a dangerous situation," said Stacie Shih with the San Jose Police Department.
The suspect, 36-year old Payam Afsari, is charged with assault with a deadly weapon and child abuse.
Police want to talk to the child to help them fully understand what happened.
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