CHICAGO (CBS) — Students at a far northwest suburban elementary school were kept in their classrooms today — after a used shell casing was found in the school.

The casing from a .22 was found on the cafeteria floor at the Crosby Elementary School about 7 a.m. or 7:30 a.m., says Harvard School District Spokesman Bill Clow.

He says a member of the custodial staff found the shell casing.

Clow says students were kept in their classrooms while a walk-through inspection was done.

He says nothing was found and Crosby Elementary, which is kindergarten through third grade, went back to business as usual for the 700 students.

Clow says the Harvard School District is doing a “precautionary walk-through” at every school in the district.

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