CONCRETE — Three pre-teen boys may have caused the five-alarm blaze Sunday that gutted the town’s historic former school house leaving an empty concrete shell, authorities said today.

The Skagit County Sheriff’s Office said that the Concrete boys, ages 11 and 12, told officers that they had started a small fire in a mattress inside the building. The boys said that they thought they had extinguished the fire before they left, according to a press release from Will Reichardt, chief criminal deputy for the Sheriff’s Office.

Investigators have referred charges to the Skagit County prosecutor for reckless burning in the 1st degree and burglary in the 2nd degree, the release said, adding that the young ages of the boys may be a factor in consideration of any charges.

The blaze was battled for several hours by crews from Concrete, Burlington and Sedro-Woolley as well as those from Punkin Center, Birdsview and Grassmere.