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PHILADELPHIA (CBS) — Police say a 10-year-old boy has been detained at Thomas G. Morton Elementary School in the Elmwood section of Philadelphia after turning in a gun to a staff member.

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The incident caused the school to be briefly placed on lockdown for about an hour on Friday morning.

Police say the boy told authorities that he found the unloaded gun in his 7-year-old sister’s book bag while in the lunch room.

No injuries were reported.

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Police are still investigating the incident.