LAWRENCE, Mass. (AP) — The Massachusetts fire marshal says an apartment fire that killed two boys was an accident caused by an electrical wiring failure.

Fire Marshal Stephen Coan says the boys were found Tuesday in a third-floor bedroom at the back of the six-unit building in Lawrence.

The blaze was reported at about 3 a.m. Video showed flames shooting from the roof.

Coan says the fire started in a ceiling space and burned undetected before breaking through the rear of the building. The building had a hard-wired alarm system in common areas and battery-powered smoke alarms in the apartments.

Fire Chief John Marsh says a firefighter was injured trying to reach the boys. Officials haven’t released their names and ages.

Mayor Daniel Rivera says the city will help the affected families.

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