MODESTO (CBS13) – Investigators are saying arson is to blame for a late December fire that caused $1.5 million in damage to a Modesto elementary school.

CBS13 reported the fire happened on Dec. 29 at Bret Harte Elementary School. The Modesto Fire Department says firefighters got to the scene just before 4 p.m. that day and found a detached wing of the school quickly going up in smoke.

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In total, the fire destroyed the school’s library, computer lab and two fifth-grade classrooms.

An adjacent wing also suffered heat damage, firefighters say.

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On Friday, Modesto Fire announced the results of their investigation. Exactly where the fire started has not been determined, but investigators have ruled it was intentionally set.

Three juveniles were interviewed during the investigation. Investigators say the kids have been referred to the district attorney’s office and could face charges. It was unclear if the kids are students at the school.

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School officials say the campus will reopen on Jan. 16 after winter break.