A 5-year-old Missouri boy found a handgun and accidentally shot and killed his infant brother.

The boys’ mother initially told Nodaway County sheriff’s deputies the older boy had shot his 9-month-old brother in the head with a paintball gun, reported WDAF-TV.

But deputies determined the boy had found a loaded .22-caliber Magnum revolver on a shelf built into the headboard of the master bed.

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The infant was in a playpen in the same room when he was shot, reported KCTV-TV.

The gun belonged to another family member and not the mother, authorities said.

A neighbor said the mother was at the family’s rural Elmo home at the time with her four sons, including a 3-year-old and 1-year-old.

The county prosecutor will assemble a child fatality review board made up of law enforcement, social workers, and medical providers to determine whether charges will be filed against the boys’ parents.

Watch this video report posted online by WDAF-TV: